Putin puts nuclear forces on alert, citing NATO threat and sanctions

Russian President Vladimir Putin ordered his military command to put nuclear-armed forces on high alert on Sunday as Ukrainian fighters defending the city of Kharkiv said they had repelled an attack by invading Russian troops.

U.S. Ambassador to the United Nations Linda Thomas-Greenfield said that "President Putin is continuing to escalate this war in a manner that is totally unacceptable and we have to continue to stem his actions in the strongest possible way."

On the fourth day of the biggest assault on a European state since World War II, the Ukrainian president's office said negotiations between Kyiv and Moscow would be held at the Belarusian-Ukrainian border. They would meet without preconditions, it said.

Thousands of Ukrainian civilians, mainly women and children, were fleeing from the Russian assault into neighboring countries.

The capital Kyiv was still in Ukrainian government hands, with President Volodymyr Zelenskyy rallying his people despite Russian shelling of civilian infrastructure.

But Putin, who has described the invasion as a "special military operation," thrust an alarming new element into play on Sunday when he ordered Russia's deterrence forces — a reference to units which include nuclear arms — onto high alert.

He cited aggressive statements by NATO leaders and economic sanctions imposed by the West against Moscow.

"As you can see, not only do Western countries take unfriendly measures against our country in the economic dimension — I mean the illegal sanctions that everyone knows about very well — but also the top officials of leading NATO countries allow themselves to make aggressive statements with regards to our country," Putin said on state television.

Russian soldiers and armored vehicles rolled into Kharkiv, Ukraine's second largest city, and witnesses reported firing and explosions.

But city authorities said Ukrainian fighters had repelled the attack.

"Control over Kharkiv is completely ours! The armed forces, the police, and the defence forces are working, and the city is being completely cleansed of the enemy," regional Gov. Oleh Sinegubov said.

Reuters was unable to immediately corroborate the information.

Ukrainian forces were also holding off Russian troops advancing on Kyiv.

"We have withstood and are successfully repelling enemy attacks. The fighting goes on," Zelenskyy said in a video message from the streets of Kyiv.

But Zelenskyy said the night had been brutal, with shelling of civilian infrastructure and attacks on everything, including ambulances.

In other developments, Russian troops blew up a natural gas pipeline in Kharkiv before daybreak, a Ukrainian state agency said, sending a burning cloud up into the darkness. Ukraine's gas pipeline operator said the transit of Russian gas to Europe via Ukraine was going on as normal.

A Russian missile strike also set an oil terminal ablaze in Vasylkiv, southwest of Kyiv, the town's mayor said.

"The enemy wants to destroy everything," said Mayor Natalia Balasinovich.

Russian-backed separatists in the eastern province of Luhansk said a Ukrainian missile had blown up an oil terminal in the town of Rovenky.

Ukraine's Western allies ratcheted up their response to Russia's land, sea and air invasion with an almost blanket ban on Russian airlines using European airspace.

In the strongest economic sanctions yet on Moscow, the United States and Europe said on Saturday they would banish big Russian banks from the main global payments system and announced other measures aimed at limiting Moscow's use of a $630 billion war chest of central bank reserves.

"We are resolved to continue imposing costs on Russia that will further isolate Russia from the international financial system and our economies," said a statement from the United States, France, Germany, Canada, Italy, Britain and the European Commission.

After initially shying away from such a move largely because of concern about the impact on their economies, the allies said they committed to "ensuring that selected Russian banks are removed from the SWIFT messaging system."

They did not name the banks that would be expelled, but an EU diplomat said some 70% of the Russian banking market would be affected.

The decision — which the French finance minister had called a "financial nuclear weapon" because of the damage it would inflict on the Russian economy — deals a blow to Russia's trade and makes it harder for its companies to do business.

SWIFT, a secure messaging network that facilitates rapid cross-border payments, said it was preparing to implement the measures.

Google barred Russia's state-owned media outlet RT and other channels from receiving money for ads on their websites, apps and YouTube videos, similar to a move Facebook made.

In the Nordic countries, Sweden, Finland and Denmark said they were preparing to close their airspace to Russian planes on Sunday, joining a string of European countries taking this measure after Russia's invasion.

The moves follow similar closures of airspace of Britain, Poland, Bulgaria, Czech Republic and Romania to Russia's aircraft. Baltic countries Lithuania, Latvia and Estonia are also closing their airspace to Russian airliners, while Germany said it was preparing to do so.

At the Vatican, Pope Francis on Sunday called for humanitarian corridors to help refugees out of Ukraine and said those who make war should not be deluded into thinking that God is on their side.

Speaking to people in St. Peter's Square, some holding large Ukrainian flags, Francis also said his "heart is broken" by the war and condemned those who "trust in the diabolic and perverse logic of weapons".

Earlier, the Kremlin said its troops were advancing again "in all directions" after Putin ordered a pause on Friday. Ukraine's government said there had been no pause.

A Ukrainian presidential adviser said about 3,500 Russian soldiers had been killed or wounded. Western officials have said intelligence showed Russia suffering higher casualties than expected.

Russia has not released casualty figures and it was impossible to verify tolls or the precise picture on the ground.

A United Nations relief agency said as of Saturday evening at least 64 civilians had been killed among 240 civilian casualties, more than 160,000 people had been internally displaced and more than 116,000 had fled to neighboring countries.

Ukraine, a democratic nation of 44 million people, won independence from Moscow in 1991 after the fall of the Soviet Union and wants to join NATO and the EU, goals Russia opposes.

Putin has said he must eliminate what he calls a serious threat to his country from its smaller neighbor, accusing it of genocide against Russian-speakers in eastern Ukraine — something Kyiv and its Western allies reject as a lie.

U.N. refugee chief Filippo Grandi said more than 150,000 Ukrainian refugees have crossed into Poland, Hungary, Moldova and Romania.

In Russia, police detained more than 900 people at anti-war protests that occurred in 44 cities on Sunday, raising the total since the start of the invasion of Ukraine on Feb. 24 to over 4,000, independent protest monitoring group OVD-Info said.

Sunday's protests coincided with the seventh anniversary of the murder of opposition politician Boris Nemtsov. Some of Sunday's arrests took place at an improvised memorial just outside the Kremlin at the site where Nemtsov was shot, a Reuters witness said.

The OVD-Info monitor has documented crackdowns on Russia's opposition for years.

Nemtsov was a prominent critic of President Vladimir Putin, Russia's annexation of Crimea in 2014 and Moscow's support for pro-Russian separatists in Ukraine, which ultimately led to Putin labels a "special operation" to protect the two separatist regions, although his troops are fighting in wider Ukraine.

More than 100,000 people protested in solidarity with Ukraine in Berlin on Sunday, after thousands rallied on Saturday in places from Sydney to Lisbon and Washington, and with more anti-war protests planned in the afternoon.