President Trump raised the prospect of attending negotiations himself, after Ukraine’s leader said he would go in person and challenged Russia’s to do the same.

The president said he's optimistic about Thursday's expected talks between Vladimir Putin and Volodymyr Zelensky in Istanbul.

The high-stakes diplomatic standoff intensifies as Zelensky insists on Putin's presence at peace negotiations, while Moscow's ambiguous response leaves the possibility of direct talks hanging in the balance.