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KYIV, Ukraine — A Russian attack at Europe’s biggest nuclear power plant in Ukraine did not result in any radiation being released and firefighters extinguished a blaze at the facility, U.N. and Ukrainian officials said, as Russian forces pressed their campaign Friday to cripple the country despite global condemnation.

The International Atomic Energy Agency’s director-general, Rafael Mariano Grossi, said Friday the building hit by a Russian “projectile” at the Zaporizhzhia plant was “not part of the reactor” but instead a training center.

Nuclear officials from Sweden to China said no radiation spikes had been reported, as did Grossi. Ukrainian officials have said Russian troops took control of the overall site, but the plant’s staff were continuing to ensure its operations. Grossi said the Ukrainians were in control of the reactor.

Still, the attack caused worldwide concern, and evoked memories of the world’s worst nuclear disaster at Ukraine’s Chernobyl.

The plant fire came as the Russian military advanced on a strategic city on the Dnieper River near where the facility is located, and gained ground in their bid to cut the country off from the sea. That would deal a severe blow to Ukraine’s economy and could worsen an already dire humanitarian situation.

With the invasion in its second week, another round of talks between Russia and Ukraine yielded a tentative agreement to set up safe corridors to evacuate citizens and deliver humanitarian aid. The war has sent more than 1 million fleeing over the border and countless others sheltering underground. A handful cities are without heat and at least one is struggling to get food and water.

There were initially conflicting reports about which part of the Zaporizhzhia plant was affected by the attack — confusion that underscored the dangers of active fighting near a nuclear power plant. It was the second time since the invasion began just over a week ago that concerns about a potential nuclear accident materialized, following a battle at Chernobyl.

Grossi said only one reactor of six at the plant is currently operating, at about 60% capacity, and that two people were injured in the fire. Ukraine’s state nuclear plant operator Enerhoatom said three Ukrainian soldiers were killed and two wounded.

Facing worldwide indignation, Russia sought to deflect blame. Without producing evidence, Defense Ministry spokesman Igor Konashenkov claimed a Ukrainian “sabotage group” had occupied the training building, fired on a Russian patrol and set fire to the building as they left.

Russia has faced increasing criticism to the invasion itself. The West has heaped sanctions on Moscow, and most of the world demanded Russia withdraw its troops in a vote in the U.N. General Assembly this week. In the latest show of international opposition, the U.N.’s top human rights body voted 32-2 on a resolution that would set up a panel of experts to monitor human rights in Ukraine. Only Russia and Eritrea opposed; 13 nations abstained.

But Russian President Vladimir Putin’s forces put pressure on cities in both the north and south.

In the center of the capital of Kyiv, frequent shelling could be heard Friday, although more distant than in recent days, with loud thudding every 10 minutes resonating over the rooftops.

Battles involving airstrikes and artillery continued Friday northwest of Kyiv and the northeastern cities of Kharkiv and Okhtyrka came under heavy strikes, Ukrainian presidential adviser Oleksiy Arestovich said.

He said Ukrainian defense forces were still holding the northern city of Chernihiv, and had prevented Russian efforts to take the important southern city of Mykolaiv. Ukrainian artillery defended Odesa from repeated attempts by Russian ships to fire on the Black Sea port, Arestovic said.

Overall, the outnumbered, outgunned Ukrainians have put up stiff resistance, staving off the swift victory that Russia appeared to have expected.

But in a sign of how much pressure they are under, Ukraine’s defense minister said Friday that the flagship of its navy was scuttled at the shipyard where it was undergoing repairs to keep it from being seized by Russian forces.

“It is hard to imagine a more difficult decision for a courageous soldier and crew,” said Oleksii Reznikov.

Another strategic port, Mariupol on the Azov Sea, was “partially under siege,” and Ukrainian forces were pushing back efforts to surround the city, Arestovich said Friday.

“The humanitarian situation is tense,” he told reporters, adding that Ukrainian authorities are in talks with Russian representatives and international organizations to set up humanitarian corridor to evacuate residents and supply food.

Battles have knocked out the city’s electricity, heat and water systems, as well as most phone service, officials said. Food deliveries were also cut.

Ukraine’s state emergency agency issued mass text messages Friday with advice on what to do in case of an explosion: Lie on the ground and cover your head with your hands; use available shelter; do not rush to leave the shelter; help the wounded; do not enter damaged buildings.

Putin’s forces have brought their superior firepower to bear over the past few days, launching hundreds of missiles and artillery attacks on cities and other sites and making significant gains in the south, including taking the port of Kherson, the first major city to fall.

Russia’s 2014 seizure of the Crimean Peninsula also gives it a logistical advantage in the country’s south, with shorter supply lines that smoothed the offensive there, said a senior U.S. defense official on condition of anonymity.

The attack on the nuclear facility led to phone calls between Ukrainian President Volodymyr Zelenskyy and U.S. President Joe Biden and other world leaders. The U.S. Department of Energy activated its nuclear incident response team as a precaution.

In an emotional speech in the middle of the night, Zelenskyy said he feared an explosion that would be “the end for everyone. The end for Europe. The evacuation of Europe.”

But most experts saw nothing to indicate impending disaster.

“The real threat to Ukrainian lives continues to be the violent invasion and bombing of their country,” the American Nuclear Society said.

Ukrainian leaders called on people to defend their homeland by cutting down trees, erecting barricades and attacking enemy columns from the rear. In recent days, authorities have issued weapons to civilians and taught them how to make Molotov cocktails.

As Russian and Ukrainian negotiators met in Belarus Thursday, Putin spoke to French President Emmanuel Macron, emphasizing that Ukraine must quickly accept the Kremlin’s demand for its “demilitarization” and declare itself neutral, renouncing its bid to join NATO.

The two sides said they tentatively agreed to allow cease-fires in areas designated safe corridors, and that they would seek to work out the necessary details quickly. A Zelenskyy adviser said a third round of talks would be held early next week.

The Pentagon set up a direct communication link to Russia’s Ministry of Defense earlier this week to avoid the possibility of a miscalculation sparking conflict between Moscow and Washington, according to a U.S. defense official who spoke on condition of anonymity because the link had not been announced.