rave Ukrainian forces have fought back against Russian troops as they invaded the capital Kyiv overnight.
Street fighting broke out in several locations and officials urged residents to take shelter and stay away from windows as enemy soldiers shelled the city.
Images of exploding bombs lighting up the night sky emerged overnight, while Ukrainians woke up to damaged buildings and unexploded shells in the streets.
A missile hit a high-rise building on the south-western outskirts of Kyiv.
People sheltered in metro stations for a second night with one 23-year-old woman giving birth to a baby daughter.
UK Armed Forces Minister James Heappey has said that Ukrainian forces defending Kyiv have been putting up “incredible resistance”.
Mr Heappey said the situation was “very grave” but that the fighting in the capital was so far confined to “very isolated pockets of Russian special forces and paratroopers”.
“The main armoured columns approaching Kyiv are still some way off. That is a testament to the incredible resistance the Ukrainian armoured forces have put up over the last 48 hours or so,” he told Sky News.
“Clearly the Russian plan is to take Kyiv but the reality is that the Ukrainians are thwarting them thus far.”
The Ministry of Defence has said that the Russian advance into Ukraine has temporarily slowed, probably because of logistical problems and strong resistance.
“The capture of Kyiv remains Russia’s primary military objective,” the ministry added.
Ukrainian President Volodymyr Zelensky offered renewed assurance Saturday that the country’s military would stand up to the Russian invasion.
In a video recorded on a downtown Kyiv street, he said he had not left the city and that claims the Ukrainian military would put down arms were false.
“We aren’t going to lay down weapons. We will protect the country,” the Ukrainian president said.
“Our weapon is our truth, and our truth is that it’s our land, our country, our children. And we will defend all of that.”
Mr Zelensky had earlier refused a US offer to be evacuated from Kyiv, telling officials “the fight is here”.
The Duke and Duchess of Cambridge are among the latest public figures to pledge solidarity with the people of Ukraine.
In a personal tweet signed by the couple, they wrote: “In October 2020 we had the privilege to meet President Zelensky and the First Lady to learn of their hope and optimism for Ukraine’s future.
“Today we stand with the President and all of Ukraine’s people as they bravely fight for that future.”
Early on Saturday French authorities seized a Russian cargo ship suspected of violating trade sanctions in the English Channel.
The US believes Russian President Vladimir Putin is determined to overthrow Ukraine’s government and replace it with a regime of his own.
Western allies have imposed strict sanctions on Russia, but they show little sign of stopping Mr Putin’s attack.
Saturday’s street clashes followed two days of massive air and missile strikes that Russian officials said targeted Ukrainian military facilities as their ground troops moved in from the north, east and south.
The assault pummelled bridges, schools and apartment buildings, and resulted in hundreds of casualties.
City officials in Kyiv urged residents to seek shelter, to stay away from windows and to take precautions to avoid flying debris or bullets.
Presidential adviser Mykhailo Podolyak said Ukrainian forces controlled the situation when the small Russian units tried to infiltrate Kyiv.
It is unclear how much of Ukraine was still under Ukrainian control and how much Russian forces have seized.
In eastern Ukraine newborn babies were moved to a makeshift bomb shelter from a neonatal intensive care unit in Dnipro in order to protect them from shells.
Dr Denis Surkov, chief of the neonatal until a Dnipropetrovsk Oblast Children’s Clinic hospital, said: “This is our reality.”
Russia has claimed to have captured the city of Melitopol in Ukraine’s southern region of Zaporizhzhya.
Melitopol is a mid-size city near the key Ukrainian port of Mariupol.
The United States and other global powers moved to freeze the assets of Putin and his foreign minister Friday as part of tougher sanctions on Russia as the invasion reverberated through the world’s economy and energy supplies.
Sports leagues also sought to punish Russia, and even the popular Eurovision song contest banned Russian acts from the event’s May finals in Italy.
Poland is refusing to play its World Cup qualifier against Russia next month in response to the invasion.
Russia has also been stripped of hosting the Champions League final by Uefa with St Petersburg replaced by Paris, and Formula One dropped this season’s Russian Grand Prix in Sochi in September.
Through it all, Russia remained unbowed, vetoing a U.N. Security Council resolution demanding that it stop attacking Ukraine and withdraw troops immediately.
The veto was expected, but the U.S. and its supporters argued that the effort would highlight Moscow’s international isolation.
The 11-1 vote, with China, India and the United Arab Emirates abstaining, showed significant opposition to the invasion.
NATO, meanwhile, decided to send parts of the alliance’s response force to help protect member nations in the east for the first time.
NATO did not say how many troops would be deployed but added that it would involve land, sea and air power.
It was unclear how many people overall had died in the largest ground war in Europe since World War II.
Ukrainian officials reported at least 137 deaths on their side from the first full day of fighting and claimed hundreds on the Russian one. Russian authorities released no casualty figures.
U.N. officials reported that 120,000 people were believed to have left Ukraine heading for Poland, Moldova and other neighbouring nations.
Russia-Ukraine crisis: Ukrainian evacuation – In pictures
They estimate that up to 4 million could flee if the fighting escalates.
Men of military age have been banned from leaving the country so most of those who crossed borders were women, children and the elderly.
Cars were backed up for several miles at some border crossings as authorities in Poland, Slovakia, Hungary, Romania and Moldova mobilised to receive the Ukrainians, providing shelter, food and legal help.
These countries also eased their usual border procedures, including Covid-19 testing requirements.
Late Friday, U.S. President Joe Biden signed a memo authorising up to $350 million (£261 million) in additional security assistance to Ukraine.
Putin has argued that the West left him with no other choice than to invade Ukraine by refusing to negotiate Russia’s security demands.