Kyiv (AFP) - Ukrainian forces repulsed a Russian attack on Kyiv but "sabotage groups" infiltrated the capital, officials said Saturday as a defiant President Volodymyr Zelensky vowed Ukraine would never give in.

On the third day of an invasion that Ukraine said has killed 198 civilians including three children, Russia also brushed off the barrage of Western sanctions and said it had fired cruise missiles at military targets.

Wearing olive green military-style clothing and looking tired but determined, Zelensky spoke in a video message posted on his Twitter account.

"I am here. We will not lay down any weapons. We will defend our state, because our weapons are our truth," he said.

"Our truth is that this is our land, our country, our children and we will protect all of this."

Russian President Vladimir Putin unleashed a full-scale invasion that has forced tens of thousands to flee their homes and sparked fears of a wider conflict in Europe.

"We thought something like this might happen but we were hoping until the end that it wouldn't," Irina Butyak, a 38-year-old teacher, told AFP as she took shelter in a basement in Kyiv, where explosions were heard through the night.

"We were hoping that common sense and common decency would prevail. Well, it didn't," said Butyak, who hoped she would be able to escape soon to western Ukraine.

In Paris, French President Emmanuel Macron warned that the world must brace for a long war.

"This crisis will last, this war will last and all the crises that come with it will have lasting consequences," Macron said, adding: "We must be prepared".

After speaking to Macron, Zelensky tweeted to thank "partners" for sending weapons and equipment.

"The anti-war coalition is working," he said.

Clashes in the Capital

AFP reporters in Kyiv heard occasional blasts of what soldiers said were artillery and Grad missiles being fired in an area northwest of the city centre.

There were also loud explosions in the centre.

Emergency services said a high-rise apartment block was hit by shelling overnight, posting a picture that showed a hole covering at least five floors blasted into the side of the building. Kyiv's mayor, Vitaly Klitschko, said that the building had been hit by a missile.

"The night was difficult, but there are no Russian troops in the capital," he said.

"The enemy is trying to break into the city, in particular from Gostomel, Zhytomyr, where the aggressors are neutralized," he said, referring to two settlements to the northwest and west of the city.

"Now in Kyiv there are, unfortunately, sabotage groups, there were several clashes, shootings," he said.

In a northern district of the city, AFP on Friday saw a dead man in civilian clothes lying sprawled on the pavement as nearby medics rushed to help another man whose car was crushed by an armoured vehicle.

Ukraine's defense ministry said "two enemy targets were shot down" -- identifying them as a Russian SU-25 helicopter and a military bomber -- near the separatist zone in the east of the country.

A Russian Ilyushin Il-76 transport plane had also been "knocked down" near Vasylkiv, a town roughly 30 kilometres (19 miles) southwest of Kyiv, the ministry added on its official Facebook page.

Zelensky's aide Mykhailo Podolyak said more than 3,500 Russian soldiers had been killed and nearly 200 captured, without providing evidence.

Moscow has yet to report on casualties

The United States, Canada, Britain and the European Union doled out further sanctions on Russia on Friday, including against Putin himself and Foreign Minister Sergei Lavrov.

Russia said the sanctions against the pair were "a demonstration of the complete impotence of the foreign policy" of the West.

"We have reached the line after which the point of no return begins," Russian foreign ministry spokeswoman Maria Zakharova said.

Moscow also vetoed a UN Security Council resolution that deplored "in the strongest terms" Russia's invasion, while China, India and the United Arab Emirates abstained.

While sanctions have focused on finances, travel and the economy, there have also been repercussions in the worlds of culture and sports.

In the latest development, Poland on Saturday said it would refuse to play its 2022 World Cup play-off against Russia on March 24.

But, despite Zelensky calling on Western allies to expel Moscow from the SWIFT banking transfer system, numerous EU countries, including Germany, Hungary and Italy, have been reluctant over fears Russia could cut off gas supplies.

Tens of Thousands Fleeing

When he announced the assault in a pre-dawn television statement on Thursday, Putin called it a "special military operation" aimed at defending Russia-backed separatists in the east.

Russia's communications regulator on Saturday told independent media to remove reports describing it as an "assault, invasion, or declaration of war".

In a statement, Roskomnadzor accused the media outlets of spreading "unreliable socially significant untrue information" about the shelling of Ukrainian cities by the Russian army and civilian deaths.

The conflict has rattled eastern members of the EU and the US-led military alliance NATO which were once dominated by Moscow.

NATO said it was deploying its rapid response forces for the first time to bolster defences on its eastern flank.

Meanwhile, Poland has been taking in thousands of Ukrainian refugees who have been arriving by train, in cars and on foot in the border city of Przemysl.

Polish Deputy Interior Minister Pawel Szefernaker on Saturday said 100,000 people have crossed the border.

"From the onset of warfare in Ukraine through today, along the entire border with Ukraine, 100,000 people have crossed the border from Ukraine into Poland," Szefernaker told reporters in the border village of Medyka, southeastern Poland.

The UN said more than 50,000 Ukrainians had fled the country in the past two days, calling for "safe unimpeded access" for aid operations.

About 100,000 people are believed to be internally displaced.