KYIV, Ukraine (AP) -- Ukrainian President Volodymr Zelenskyy called on people worldwide to gather in public Thursday to show support for his embattled country as U.S. President Joe Biden and other world leaders met for talks focused on pressuring Russia to end the invasion that is entering its second month.
"Come to your squares, your streets. Make yourselves visible and heard," Zelenskyy 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."
Brussels was the center Thursday of a flurry of diplomatic activity. NATO Secretary-General Jens Stoltenberg opened an emergency summit bringing together Biden and other leaders by saying that the alliance is determined to continue to ratchet up the costs on Russia for its aggression.
Russia unleashed its invasion Feb. 24 in Europe's biggest offensive since World War II, but instead of swiftly toppling Ukraine's government, its forces are bogged down in a grinding military campaign and its economy is laboring under punishing international sanctions.
The Russian stock market resumed limited trading Thursday under heavy restrictions almost one month after prices plunged and the market was shut down following the invasion. Trading of a limited number of stocks including energy giants Gazprom and Rosneft took place under curbs that are meant to prevent a repeat of the massive selloff that took place Feb. 24 in anticipation of Western economic sanctions. Foreigners cannot sell and traders are barred from short selling, or betting prices will fall. The benchmark MOEX index gained 8% in the first minutes of trading.
Ukraine's navy reported Thursday that it had sunk the Russian ship Orsk in the Sea of Asov near the port city of Berdyansk. It released photos and video 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 since Feb. 27, and the Orsk had debarked armored vehicles there on Monday for use in Moscow's offensive, the Zvezda TV channel of the Russian Defense Ministry said earlier this week. According to the report, the Orsk was the first Russian warship to enter Berdyansk, which is about 80 kilometers (50 miles) west along the coast from the besieged city of Mariupol.
To keep up the pressure on Russia, Zelenskyy said he would ask in a video conference with NATO members that the alliance provide "effective and unrestricted" support to Ukraine, including any weapons the country needs.
Biden was expected to discuss new sanctions and how to coordinate 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.
On the eve of the meetings, European Union nations signed off on another 500 million euros ($550 million) in military aid for Ukraine.
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.
In its last update March 2, Russia said that nearly 500 of its soldiers had been killed and almost 1,600 wounded. NATO estimates, however, that between 7,000 and 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 Zelenskyy said nearly two weeks ago that about 1,300 Ukrainian troops had been killed.
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.
U.S. officials long have warned that Russia's military doctrine envisages an "escalate to deescalate" option of using battlefield nuclear weapons to force the enemy to back down in a situation when Russian forces face imminent defeat. Moscow has denied having such plans.
Rogozin, known for his bluster, did not make clear what actions by the West would be seen as meddling, but his comments almost certainly reflect thinking inside the Kremlin. Putin has warned the West that an attempt to introduce a no-fly zone over Ukraine would draw it into a conflict with Russia. Western nations have said they would not create a no-fly zone to protect Ukraine.
Zelenskyy noted in his national address that Ukraine has not received the fighter jets or modern air-defense 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.
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, 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 theater and an art school where civilians were sheltering.
Zelenskyy 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 governor 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 neighborhoods have been destroyed.
"I don't understand why we have such a curse," she said.