US President Joe Biden said Russia was deliberately targeting civilians in Ukraine, but did not call it a war crime.

"It is clear that they are targeting civilians," Biden said. Asked whether he thought Russia was committing war crimes, Biden said: "We are following it very closely. It’s early to say that.”

Biden also confirmed that sanctions on Russian oil exports were still possible, although officials warned that they would work to minimise the impact of such a move on US and global oil prices. "Nothing is off the table," Biden said.

He also said that Ukrainian leader Volodymyr Zelenskyy should decide for himself whether he wants to stay in his country. "It's his judgment to make and we're doing everything we can," he said.

CNN earlier reported that the US had discussed contingency plans with Zelenskyy to leave Ukraine or move to Lviv. Zelenskyy has repeatedly said that he would stay in the capital.