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.

Ukrainian and Russian officials ended their third round of peace negotiations in under an hour Wednesday — falling short of establishing a cease-fire but agreeing to a prison swap. The talks took place in Istanbul just over a week after President Trump threatened Russian President Vladimir Putin with “very severe tariffs” if he doesn’t commit to a cease-fire in Ukraine within 50 days.

Russian and Ukrainian delegates concluded their third set of direct talks in Istanbul “about 40 minutes” after they started, the Russian state news agency TASS reported Wednesday, citing a source.