KYIV. Missiles pounded the Ukrainian capital on Friday as Russian forces pressed their advance and Ukrainian President Volodymyr Zelenskiy pleaded with the international community to do more, saying sanctions announced so far were not enough.

Air raid sirens wailed over the city of 3 million people, where some were sheltering in underground metro stations, a day after Russian President Vladimir Putin launched an invasion that has shocked the world. A Ukrainian official said a Russian plane had been shot down and crashed into a building.

A senior Ukrainian official said Russian forces would enter areas just outside the capital, Kyiv, later on Friday and that Ukrainian troops were defending positions on four fronts despite being outnumbered.

An estimated 100,000 people fled as explosions and gunfire rocked major cities. Dozens have been reported killed. Russian troops seized the Chernobyl former nuclear power plant north of Kyiv as they advanced on the city from Belarus.

US and Ukrainian officials say Russia aims to capture Kyiv and topple the government, which Putin regards as a puppet of the United States.

Zelenskiy said he understood Russian troops were coming for him but vowed to stay in Kyiv.

"(The) enemy has marked me down as the number one target," Zelenskiy said in a video message. "My family is the number two target. They want to destroy Ukraine politically by destroying the head of state."

"I will stay in the capital. My family is also in Ukraine."

Russia launched its invasion by land, air and sea on Thursday following a declaration of war by Putin, in the biggest attack on a European state since World War Two.

Putin says Russia is carrying out "a special military operation" to stop the Ukrainian government from committing "genocide" - an accusation the West calls a baseless fabrication. He says Ukraine is an illegitimate state whose lands historically belong to Russia, a view which Ukrainians see as an attempt to erase their more than thousand year history.

Putin's full aims remain obscure. He has said he does not plan a military occupation, only to disarm Ukraine and remove its leaders. But having told Ukrainians their state is illegitimate, it is hard to see how he could simply impose a new leader and withdraw. Russia has floated no name of a figure it would regard as acceptable and none has come forward.

Britain said Moscow's aim was to conquer all of Ukraine, and its military had failed to meet its main objectives on the first day because it failed to anticipate Ukrainians would resist.

"It's definitely our view that the Russians intend to invade the whole of Ukraine," Defence Secretary Ben Wallace told Sky.

"Contrary to great Russian claims - and indeed President Putin's sort of vision that somehow the Ukrainians would be liberated and would be flocking to his cause - he's got that completely wrong, and the Russian army has failed to deliver, on day one, its main objective."

Ukrainians were circulating an unverified recording on Friday of a Russian warship ordering Ukrainian troops at a Black Sea outpost to surrender. The Ukrainians reply: "Russian warship, go fuck yourself." Zelenskiy said the 13 men were killed by a Russian strike and would receive posthumous honours.

Ukrainian forces downed an enemy aircraft over Kyiv early on Friday, which then crashed into a residential building and set it ablaze, said Anton Herashchenko, an adviser to the interior minister.

It was unclear whether the aircraft was manned or whether it could be a missile. Kyiv municipal authorities said at least eight people were injured when the object crashed into an apartment block.

'Horrific'

"Horrific Russian rocket strikes on Kyiv," Foreign Minister Dmytro Kuleba wrote on Twitter. "Last time our capital experienced anything like this was in 1941 when it was attacked by Nazi Germany."

Authorities said intense fighting was under way in the city of Sumy in the northeast.

A border post in the southeast had been hit by missiles, causing deaths and injuries among border guards, and air raid sirens sounded over the city of Lviv in the west of the country.

Asked if he was worried about Zelenskiy's safety, US Secretary of State Antony Blinken told CBS: "To the best of my knowledge, President Zelenskiy remains in Ukraine at his post, and of course we're concerned for the safety of all of our friends in Ukraine - government officials and others."

Sanctions build

A democratic nation of 44 million people, Ukraine voted for independence at the fall of the Soviet Union and has recently stepped up efforts to join the NATO military alliance and the European Union, aspirations that infuriate Moscow.

Western countries unveiled financial sanctions on Moscow billed as far stronger than earlier measures, including blacklisting its banks and banning technology imports. However, they stopped short of forcing Russia out of the SWIFT system for international bank payments, drawing strong words from Kyiv which says the most serious steps should be taken now.

The UN Security Council will vote on Friday on a draft resolution that would condemn the invasion and require Moscow's immediate withdrawal, though Moscow is certain to veto it. China, which signed a friendship treaty with Russia three weeks ago, has refused to describe Moscow's actions as an invasion.

Russia is one of the world's biggest energy producers, and both it and Ukraine are among the top exporters of grain. War and sanctions will disrupt economies around the world.

Oil and grain prices have soared. Share markets around the world, many of which plunged on Thursday at news of the outbreak of war, were mainly rebounding on Friday.