US President Joe Biden told Ukrainian President Volodymyr Zelensky in a telephone conversation on Tuesday that his country would allocate $625 million in new security aid to Kyiv, the White House reported.

The aid will include more High Mobility Artillery Missile Systems (HIMARS), shells and armored vehicles, the White House said in a statement.

Biden "pledged to continue helping Ukraine defend itself against Russian aggression for as long as necessary," the White House said.

The US president also confirmed that the United States is ready to "impose serious costs on any person, organization or country that promotes Russia's annexation [of Ukrainian territories]".

Earlier, Zelenskyy signed a decree officially declaring that talks between Kyiv and Russian President Vladimir Putin are "impossible." 

The decree implemented a decision by Ukraine's National Security Council and Defense Council and formalised President Zelenskyy's comments after Putin declared four Ukrainian regions occupied by Moscow to be part of Russia.

On September 30, Zelenskyy said that "Putin does not know what dignity and honesty are. Therefore, we are ready for a dialogue with Russia, but with another Russian president."