Antalya, Turkey - Secretary of State Marco Rubio said Thursday he did not expect breakthroughs in talks between Ukraine and Russia, which sent a low-level delegation to Istanbul.

Rubio repeated President Donald Trump's assertion earlier in the day that a solution required talks between the US leader and Russian President Vladimir Putin, who declined to go to Turkey.

"I want to be frank. I don't think we don't have high expectations of what will happen tomorrow," Rubio told reporters after a NATO meeting in Antalya, Turkey.

Russia and Ukraine had been expected to meet on Thursday in Istanbul for their first direct peace talks in more than three years, but as the day wore on without any concrete indications of timings, it remained unclear whether they would meet later in the evening or leave it until Friday.

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Rubio acknowledged that the Russian representation was "not at the levels we had hoped it would be at".

"I hope I'm wrong. I hope they have tremendous breakthroughs tomorrow," he said.

"But I frankly, do not believe that we're going to have a breakthrough here until President Trump sits face-to-face with President Putin and determines what his intentions are moving forward," Rubio said.

Rubio said he would meet in Istanbul with Ukrainian Foreign Minister Andriy Sybiga and that a lower-level US official would meet the Russians.

Rubio voiced hope that host nation Turkey would bring the Ukrainian and Russian delegations together.