US President Donald Trump's special envoy, Steve Witkoff, flew to Russia on Friday for talks with President Vladimir Putin about the search for a peace deal on Ukraine, the Kremlin said, saying the two men might also discuss a Trump-Putin meeting.

The Izvestia news outlet released video of Witkoff leaving a hotel in Russia's second city St Petersburg, accompanied by Kirill Dmitriev, Putin's investment envoy.

Witkoff has emerged as a key figure in the on-off rapprochement between Moscow and Washington amid talk on the Russian side of potential joint investments in the Arctic and in Russian rare earth minerals.

Putin was also in St Petersburg on Friday to hold what the Kremlin called an "extraordinarily important" meeting about the development of the Russian Navy, which is in the throes of a major modernisation and expansion drive.

Kremlin spokesman Dmitry Peskov played down the planned Witkoff-Putin meeting, telling Russian state media the US envoy's visit would not be "momentous" and that no breakthroughs were expected.

U.S. President Donald Trump and Russia's President Vladimir Putin are seen during the G20 leaders summit in Buenos Aires, Argentina November 30, 2018 (credit: MARCOS BRINDICCI/REUTERS)
U.S. President Donald Trump and Russia's President Vladimir Putin are seen during the G20 leaders summit in Buenos Aires, Argentina November 30, 2018 (credit: MARCOS BRINDICCI/REUTERS)

US tensions with Iran, China

The meeting will be their third this year and comes at a time when US tensions with Iran and China - two countries with which Russia has close ties - are severely strained over Tehran's nuclear programme and a burgeoning trade war with Beijing.

Witkoff is due in Oman on Saturday for talks with Iran over its nuclear programme after Trump threatened Tehran with military action if it does not agree to a deal. Moscow has repeatedly offered its help in trying to clinch a diplomatic settlement.

Putin and Trump have spoken by phone but have yet to meet face-to-face since the US leader returned to the White House in January for a second four-year term.

Possible peace deal to end the war in Ukraine

US and Russian officials said they had made progress during talks in Istanbul on Thursday towards normalising the work of their diplomatic missions as they begin to rebuild bilateral ties.

However, US-Russia dialogue aimed at agreeing a ceasefire ahead of a possible peace deal to end the war in Ukraine appears to have stalled over disagreements around the conditions for a full pause in hostilities.

Trump, who has shown signs of losing patience, has spoken of imposing secondary sanctions on countries that buy Russian oil if he feels Moscow is dragging its feet on a Ukrainian deal.

A February meeting between Witkoff and Putin culminated with the US envoy flying home with Marc Fogel, an American teacher Washington had said was wrongfully detained by Russia.

A Russian-American spa worker Ksenia Karelina, who had been sentenced to 12 years in prison in Russia, was exchanged on Thursday for Arthur Petrov, whom the US had accused of forming a global smuggling ring to transfer sensitive electronics to Russia's military.

The US lists several Americans - some dual citizens - who are in jail in Russia, including Stephen Hubbard, another teacher whom Washington has officially declared as wrongfully detained.