The US secretary of state has called on Russia "to honour its commitments" and fully restore an oft-violated truce between Moscow-backed rebels and Ukraine's government forces, saying Washington aims "to restore Ukraine's territorial integrity and sovereignty".

Rex Tillerson said on Sunday that "it is necessary for Russia to take the first step to de-escalate the situation in the east part of Ukraine", pulling back heavy weaponry to lines agreed upon under a two-year-old accord known as the Minsk Agreement.

"We are disappointed by the lack of progress under the Minsk agreement," he said at a joint briefing with Ukrainian President Petro Poroshenko after they held talks. "We do call on Russia to honour its commitments."

He also urged the Kremlin to allow the OSCE, a pan-European security body, to carry out their responsibilities.

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Tillerson said sanctions against Russia would remain in place "until Moscow reverses its actions", including the return of the annexed Crimean peninsula.

A primary goal of the United States "is to restore Ukraine's territorial integrity and sovereignty", he said.

The conflict, which has killed at least 10,000 people, as well as Russia's annexation of Crimea from Ukraine in 2014, have pushed ties between Moscow and the West to their lowest point since the Cold War.

The US and the European Union have imposed sanctions on Russia, though Moscow has denied backing the rebels.

Tillerson's visit to Ukraine followed a first face-to-face meeting between US President Donald Trump and his Russian counterpart Vladimir Putin on Friday at the G20 summit in Hamburg, Germany.

Hawk on Russia

Poroshenko hailed US involvement and reiterated Tillerson's commitment to seeking a negotiated peace deal.

"Most of all we want peace in Ukraine. We firmly adhere to our commitments," he said.

Poroshenko was especially complimentary of Tillerson's decision last week to appoint a special envoy for Ukraine negotiations, former US ambassador to NATO Kurt Volker, who is widely considered to be a hawk on Russia.

Volker will oversee US efforts to press Ukraine and Russia to fully comply with the Minsk Agreement, the peace accord that was reached in early 2015 in the capital of Belarus by the leaders of France, Germany, Ukraine and Russia but has yet to be implemented.

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Under the Obama administration, the US had taken a hands-off approach to Minsk, allowing the Europeans to take the lead.

Speaking to a group of reform advocates at the US ambassador's residence, Tillerson praised Ukraine's progress in combating corruption but made clear that more must be accomplished.

"Ukraine has come a long way," he said. "We want to acknowledge that, [but] we still have more to do."