Joe Biden has said Vladimir Putin "cannot remain in power," appealing to the Russian people against the killing of innocent civilians, and telling Ukraine that the US stands with them.

In a powerful speech in Warsaw, Poland, the US president built on earlier remarks in which he called Mr Putin a "butcher", describing him as "a dictator" and saying stopping the war in Ukraine is "the task of our time".

He said: "Brutality will never grind down the will to be free. Ukraine will never be a victory for Russia."

"For God's sake, this man cannot remain in power," Mr Biden added at the end of his speech.

The White House later denied the US president was calling for regime change.

And a Kremlin spokesman, responding to Mr Biden's comment, said: "That's not for Biden to decide. The president of Russia is elected by Russians."

And quoting Pope John Paul II, he said: "Never, ever give up hope, never doubt, never tire, never become discouraged. Be not afraid."

Mr Biden also sent a direct message to the people of Russia to say they are "not the enemy".

He continued that "I refuse to believe that you welcome the killing of innocent children and grandparents or that you accept hospitals, schools, maternity wards, for God's sake, be pummelled with Russian missiles and bombs. Or cities being surrounded so that civilians cannot flee, supplies cut off in attempts to starve Ukrainians.

"Millions of families are being driven from their home, including half of all Ukraine's children. These are not the actions of a great nation."

The American president said "swift and punishing" costs are the only things that will get Mr Putin to change his course, a month on from the invasion of Ukraine.

He said his message to the people of Ukraine is simple: "We stand with you."

Russia, he added, had "strangled democracy" and "sought to do so elsewhere", while Mr Putin had "the gall" to say he did not invade Ukraine. Mr Biden said: "It's a lie. It's just cynical. He knows that. And it's also obscene."

Mr Biden recalled previous occasions when "Soviet tanks crushed democratic uprisings", such as in Hungary in 1956 and Czechoslovakia in 1968.

"The test of this moment", he said, is "the test of all time".

He promised the US would help Europe "end its dependence on Russian fossil fuels", as "the days of any nation being subject to the whims of a tyrant for its energy needs are over".

Mr Biden's speech ends a four-day trip that also included an earlier stop for a series of summits in Brussels.

Earlier on Saturday, following official meetings in Warsaw, the president described Mr Putin as a "butcher".

The Kremlin said his comment would further narrow any possibilities of repairing relations, according to Russian state news agency Tass.

Mr Biden and the US foreign and defence ministers Antony Blinken and Lloyd Austin met their Ukrainian counterparts for the first time to discuss how "to fortify Ukraine's ability to fight back Russian aggression".

Ukrainian foreign minister Dmytro Kuleba told reporters that Ukraine had received additional security pledges from the US on developing defence co-operation.

He also said that Ukraine agreed with the US on ways to put pressure on Europe to impose fresh sanctions on Russia.

Meanwhile, Mr Biden said he was "not sure" that Russia had changed its strategy in its invasion of Ukraine after Moscow said its focus was now to completely "liberate" the breakaway eastern Donbas region. (Courtesy, excluding headline, Sky News)

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