Ukrainian President Volodymyr Zelenskyy is applying more pressure on President Donald Trump to increase the cost of what he sees as Russian obfuscation.

Delegations from the warring sides met for barely an hour and agreed to exchange more prisoners of war - focusing on the youngest and most severely wounded - and return the bodies of 12,000 dead soldiers.

Russian and Ukrainian officials are due to hold peace talks in Istanbul with no sign they are any closer to an agreement.