I STANBUL—President Trump’s ultimatum for Russian President Vladimir Putin is showing no signs of bringing Russia and Ukraine any closer to peace. The third round of direct talks between Ukrainian and Russian officials, held Wednesday in Istanbul, yielded few results. The two sides met for less than an hour.

The two sides agreed to have a prisoner exchange of 1,200 people, National Security and Defense Council Secretary Rustem Umerov said.

During the talks, Ukraine proposed holding a summit between President Volodymyr Zelensky and Russian President Vladimir Putin before the end of August, according to National Security and Defense Council Secretary Rustem Umerov,