Talks between US and Ukrainian delegations in Saudi Arabia are going 'OK', a senior Ukrainian official said in a blunt appraisal as diplomats met for crunch talks on rebuilding bridges and ending the war with Russia.

'The talks are going OK, a lot of questions have been discussed,' the official, who requested anonymity, said in vague comments to AFP on Tuesday with talks underway in Jeddah, notably without the two presidents.

Volodymyr Zelensky sent his chief of staff, Andriy Yermak, to meet with Donald Trump's secretary of state, Marco Rubio, in the hope of building confidence following a souring of relations in recent weeks. 

The meeting marks the first high-level talks between Kyiv and Washington since Zelensky clashed with Trump during an Oval Office meeting last month.

'We are ready to do everything to achieve peace,' Yermak told reporters as he arrived for the talks. The two sides spoke for about three hours in the morning, before a break, with more planned for the afternoon.

Yermak echoed the hesitant tone of the anonymous official in a one-line post on social media later on: 'Work in progress.' 

The chief of staff's presence at the negotiating table remains a controversial decision, and could throw Kyiv's chances of securing a favourable peace deal.

That is because Donald Trump, who harbours a clear distaste for Zelensky, is believed to foster similar feelings for his top aide.

Yermak, 53, was a central figure in the Hunter Biden scandal which saw Trump accused of pressuring Zelensky to dig up dirt on Joe Biden's family in exchange for military aid - allegations that led to the US president's impeachment.

Ukrainian officials this week admitted they still think Trump bears ill will toward Yermak, though they hope US Secretary of State Marco Rubio's presence will help to calm any tensions between the two delegations.