Ukraine's navy reported on Thursday that it had destroyed the Russian landing ship Orsk in the Sea of Azov, docked at the occupied Ukrainian port city of Berdyansk.

The Navy of the Armed Forces of Ukraine released photos and video on Facebook of fire and thick smoke coming from the port area. Russia did not immediately comment on the claim.

Russia has been in possession of the port in southern Ukraine since Feb. 27 — a few days after Russia's invasion of the country began — and the Orsk had disembarked armoured vehicles there on Monday for use in Moscow's offensive, the Zvezda TV channel of the Russian Defence Ministry said earlier this week.

According to the report, the Orsk was the first Russian ship to enter Berdyansk, which is about 80 kilometres west along the coast from the besieged city of Mariupol.

When Russia unleashed its invasion Feb. 24 in Europe's biggest offensive since the Second World War, a swift toppling of Ukraine's government seemed likely. But a month into the fighting, Moscow is bogged down in a grinding military campaign of attrition after meeting fierce Ukrainian resistance.

Zelensky calls for global protest

In Kyiv, Ukrainian President Volodymr Zelensky called on people worldwide to gather in public on Thursday to show support for his embattled country as he prepared to address U.S. President Joe Biden and other NATO leaders gathered in Brussels on the one-month anniversary of the Russian invasion.

"Come to your squares, your streets. Make yourselves visible and heard," Zelensky said in English during an emotional video address late Wednesday that was recorded in the dark near the presidential offices in Kyiv. "Say that people matter. Freedom matters. Peace matters. Ukraine matters."

He also urged NATO to take "serious steps" to help Kyiv fight Russia's invasion, as an unprecedented one-day trio of NATO, G7 and EU summits got underway.

"At these three summits we will see who is our friend, who is our partner and who sold us out and betrayed us," Zelensky said.

Biden was expected to discuss new sanctions and how to co-ordinate such measures, along with more military aid for Ukraine, with NATO members, and then talk with leaders of the G7 industrialized nations and the European Council in a series of meetings on Thursday.

New U.S. military aid on its way

On the eve of the meeting with Biden, European Union nations signed off on another 500 million euros ($691 million Cdn) in military aid for Ukraine.

The first U.S. shipment from a new, $800 million US arms package for Ukraine will start flying out in the next day or so, a U.S. defence official said.

The United States plans to accept up to 100,000 Ukrainians fleeing Russia's invasion, two sources familiar with the plan told Reuters on Thursday.

The expected announcement would coincide with the U.S. president's meeting with European leaders on Thursday to co-ordinate the Western response to the crisis.

More than 3.5 million people have fled since Russia invaded Ukraine on Feb. 24, according to the United Nations.

To keep up the pressure on Russia, Zelensky spoke to NATO members in a video address on Thursday, asking the alliance to provide "effective and unrestricted" support to Ukraine, including weapons, tanks, planes, rockets and air defence systems.

Citing a long list of weaponry he said is vital for his country's survival, the Ukrainian leader asked NATO leaders for "military assistance without limitations," telling them that Ukrainian forces are "in a grey area, between the West and Russia, defending our common values."

"This is the scariest thing during a war — not to have clear answers to requests for help," Zelensky said.

In his national address late Wednesday, Zelensky said Ukraine has not received the fighter jets or modern air-defence systems it requested. He said Ukraine also needs tanks and anti-ship systems.

"It has been a month of defending ourselves from attempts to destroy us, wipe us off the face of the earth," he said.

NATO leader's term extended

Opening the NATO summit, Secretary General Jens Stoltenberg said the alliance is "determined to continue to impose costs on Russia to bring about the end of this brutal war."

Soon afterward, NATO countries extended Stoltenberg's mandate by a year to allow him to continue leading the military alliance's response to Russia's aggression.

Stoltenberg had been due to leave the post in September and had already been appointed as the next head of Norway's central bank. The Norwegian government said on Thursday that the deputy governor will be in charge until he is free to take over.

Stoltenberg on Wednesday said the alliance would boost its forces in eastern Europe by deploying four new battle groups in Bulgaria, Hungary, Romania, Slovakia.

Biden said this week that the possibility of Russia deploying chemical weapons was a "real threat."

Stoltenberg declined Thursday to discuss whether such a strike is a red line that would draw the alliance into war with Russia. "I will not speculate beyond the fact that NATO is always ready to defend, to protect and to react to any type of attack on a NATO allied country," he said.

In its last update on troop losses, Russia said on March 2 that nearly 500 of its soldiers had been killed and almost 1,600 wounded. NATO estimates, however, that between 7,000 to 15,000 Russian troops have been killed — the latter figure about what Russia lost in a decade of fighting in Afghanistan.

A senior NATO military official said the alliance's estimate was based on information from Ukrainian authorities, what Russia has released — intentionally or not — and intelligence gathered from open sources. The official spoke on condition of anonymity under ground rules set by NATO.

Ukraine also claims to have killed six Russian generals. Russia acknowledges just one dead general.

Ukraine has released little information about its own military losses, and the West has not given an estimate, but Zelensky said nearly two weeks ago that about 1,300 Ukrainian troops had been killed.

With its ground forces slowed or stopped by hit-and-run Ukrainian units armed with Western-supplied weapons, Russian President Vladimir Putin's troops are bombarding targets from afar, falling back on the tactics they used in reducing cities to rubble in Syria and Chechnya.

A senior U.S. defence official said Wednesday that Russian ground forces appear to be digging in and setting up defensive positions 15 to 20 kilometres outside Kyiv, the capital, as they make little to no progress toward the city centre.

The official, who spoke on condition of anonymity to discuss military assessments, said it appears the forces are no longer trying to advance into the city, and in some areas east of Kyiv, Ukrainian troops have pushed Russian soldiers farther away.

Instead, Russian troops appear to be prioritizing the fight in the eastern Luhansk and Donetsk regions in the Donbas, in what could be an effort to cut off Ukrainian troops and prevent them from moving west to defend other cities, the official said. The U.S. also has seen activity from Russian ships in the Sea of Azov, including what appear to be efforts to send landing ships ashore with supplies, including vehicles, the official said.

Threat of nuclear weapons

Despite evidence to the contrary, Kremlin spokesperson Dmitry Peskov insisted the military operation is going "strictly in accordance" with plans.

In an ominous sign that Moscow might consider using nuclear weapons, senior Russian official Dmitry Rogozin said the country's nuclear arsenal would help deter the West from intervening in Ukraine.

"The Russian Federation is capable of physically destroying any aggressor or any aggressor group within minutes at any distance," said Rogozin, who heads the state aerospace corporation, Roscosmos, and oversees missile-building facilities. He noted in his televised remarks that Moscow's nuclear stockpiles include tactical nuclear weapons, designed for use on battlefields, along with far more powerful nuclear-tipped intercontinental ballistic missiles.

In Kyiv, where near-constant shelling and gunfire shook the city Wednesday as the two sides battled for control of multiple suburbs, Mayor Vitali Klitschko said at least 264 civilians have been killed since the war broke out. The independent Russian news outlet The Insider said Russian journalist Oksana Baulina had been killed by shelling in a Kyiv neighbourhood on Wednesday.

Mariupol encircled but not taken

In the south, the encircled port city of Mariupol has seen the worst devastation of the war, enduring weeks of bombardment and, now, street-by-street fighting. But Ukrainian forces have prevented its fall, thwarting an apparent bid by Moscow to fully secure a land bridge from Russia to Crimea, which was seized from Ukraine in 2014.

In their last update, over a week ago, Mariupol officials said at least 2,300 people had died, but the true toll is probably much higher. Airstrikes in the past week destroyed a theatre and an art school where civilians were sheltering.

Zelensky said 100,000 civilians remain in the city, which had a population of 430,000 before the war. Efforts to get desperately needed food and other supplies to those trapped have often failed.

In the besieged northern city of Chernihiv, Russian forces bombed and destroyed a bridge that was used for aid deliveries and civilian evacuations, regional Gov. Viacheslav Chaus said.

Kateryna Mytkevich, 39, who arrived in Poland after fleeing Chernihiv, wiped away tears as she said the city is without gas, electricity or running water, and entire neighbourhoods have been destroyed.

"I don't understand why we have such a curse," she said.