The mayor of Kyiv said the city has entered a "defensive phase" as air raid sirens went off and gunfire was heard near the government district.

Russian tanks were seen just miles away and residents were told to stay home and avoid "active military operations" in the Obolon district.

Kyiv is a key focus in Russia's invasion of Ukraine, which began on Thursday and is the biggest attack on a European state since the Second World War.

Kyiv hit by 'horrific rocket strikes' as Russian invasion enters second day - live updates

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The Russian defence ministry said it has blocked the city from the West and paratroopers have taken control of an aerodome nearby, according to Russia's TASS news agency - but these reports have not been confirmed.

Since before dawn the city of three million people faced a barrage of explosions, with residents huddled in shelters.

"Horrific Russian rocket strikes on Kyiv," said Dmytro Kuleba, Ukraine's foreign minister. "Last time our capital experienced anything like this was in 1941 when it was attacked by Nazi Germany."

Photos posted by the emergency services showed a damaged residential building and Kyiv's mayor, Vitali Klitschko, said three people were injured, with one in critical condition.

Earlier on Friday Ukrainian President Volodymyr Zelenskyy - who remains in Kyiv - said 137 Ukrainians have been killed and 316 injured since the invasion began.

As missile strikes rained down on large parts of the country, he said new sanctions were not enough to stop Russia and said the world is watching what is going on in Ukraine from afar.

Ukraine's interior ministry said Russia attacked 33 civilian sites over the last 24 hours and two children were killed, according to Interfax news agency.

Russia is believed to have lost more than 450 military personnel, Defence Secretary Ben Wallace said.

US officials believe Russian President Vladimir Putin aims to dismantle the government and replace it with his own regime, while Mr Zelenskyy said he is "target number one" for Russia.

A Ukrainian government adviser said Russia plans to use tanks to break through to the capital and Ukrainian forces are ready to respond with anti-tank missiles supplied by foreign allies.

Some 100,000 Ukrainians are believed to have fled their homes, according to the United Nations, but the country's border guard service has said that males aged 18-60 are not allowed to leave.

A mass mobilisation decree was issued by Mr Zelenskyy which requires all conscripts and reservists to help "ensure the needs" of Ukraine's military, paving the way for civilians to take up arms.

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It comes after Mr Zelenskyy imposed martial law, putting the military in control of the country.

Ukraine's armed forces believe more than 60 Russian battalion tactical groups - the equivalent of between 30,000 and 60,000 troops - have been deployed.

Mr Putin is thought to be targeting a blockade of Kyiv and the creation of a land corridor on Ukraine's southeastern coast towards the Crimean Peninsula - which Moscow annexed in 2014 - and the Transdniestria region of neighbouring Moldova that is held by pro-Russian separatists.

What's happening on the ground

With Russia having seized control of Chernobyl, near Pripyat, around 60 miles from Kyiv, attention is now turning to other sites.

One that has been the scene of intense combat so far is Hostomel military airport, also near Kyiv. It could prove vital, as Russia could use it to bring more troops into the country.

Elsewhere, fierce fighting has taken place in Sumy and Kharkiv in the northeast, Kherson and Odessa in the south.

Loud blasts and a barrage of artillery were heard in Kharkiv by Sky correspondent John Sparks, who said the city is in the process of being encircled by Russian troops.

The Russian defence ministry said 118 Ukrainian military infrastructure sites have been destroyed.

Border units, border patrols and checkpoints have been targeted with artillery, heavy equipment and small arms fire, including a missile strike at a border post in the Zaporizhzhya region, Ukrainian officials said.

A US official said Russian forces were moving from annexed Crimea to Kherson in the south, from Belarus - north of Ukraine - towards Kyiv, and from the northeast to Kharkiv.

The official said as part of the "first phase" of the assault, more than 100 missiles were launched from land and sea, primarily short-range ballistic missiles, but also those of medium-range, cruise missiles, and surface-to-air missiles.

The main targets were barracks, ammunition warehouses and airfields, before ground forces moved in.

Ukraine reported columns of troops penetrated its borders into Chernihiv, Kharkiv and Luhansk in the east - and also landed by sea at the cities of Odessa and Mariupol in the south.

However, Ukrainian forces have reportedly halted Russia's advance towards Chernihiv, with fighting restricted to the outskirts of the city.

British intelligence suggests that after a day of "fierce resistance" by Ukrainian troops, it is considered "unlikely" that Russia has achieved its planned objectives for the opening 24 hours of the invasion.

Russia hit with sanctions

Later on Friday, the United Nations Security Council will vote on a resolution condemning Russia for its actions in Ukraine and calling for its immediate withdrawal.

It is doomed to fail, given Russia's veto power on the council. However, a diplomatic source in New York - where the negotiations have taken place - told Sky's Mark Stone it was "another chance to isolate Russia".

There will be particular interest in how China votes, given Beijing's foreign ministry refused to accept the reality that Russia had "invaded" Ukraine. It has instead blamed the US for "hyping up" the situation.

Boris Johnson hit Russia with what he called the "largest set of sanctions ever imposed anywhere by the UK government" - targeting more than 100 businesses and individuals.

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EU leaders also agreed to another set of sanctions, taking aim at Russia's financial, transport and energy sectors.

Ursula von der Leyen, president of the European Commission, said they included targeting 70% of the Russian banking market and key state-owned companies.

French President Emmanuel Macron, who held a "frank, direct, quick" call with Mr Putin after the invasion, said separate sanctions would be forthcoming from Paris.

Joe Biden said "strong limitations" will be imposed on what can be exported from the US to Russia.

However, the US president insisted that US troops "will not be engaged in the conflict with Russia in Ukraine", with soldiers instead deployed to eastern European NATO allies to "reassure" them.

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