WASHINGTON (AFP) - Mr Donald Trump on Thursday (May 11) urged Russia and Ukraine to "make peace", in a tweet accompanied by two photos of the United States president posing with top diplomats from the rival countries.

"Yesterday, on the same day - I had meetings with Russian Foreign Minister Sergei Lavrov and the FM of Ukraine, Pavlo Klimkin. #LetsMakePeace!" the US president tweeted.

Russia and Ukraine have been in conflict since 2014, and Russia's annexation of Crimea has been a major point of contention between Washington and Moscow.

The tweeted photos fashion a grinning Mr Trump as peacemaker, a day after the Republican leader gave Mr Lavrov a rare Oval Office welcome and Ukraine's Mr Klimkin met with Vice President Mike Pence.

A Trump-Klimkin meeting had not been on the US president's public agenda.

Mr Trump tweeted the images after the White House had been left fuming when the Russian Embassy published photos of his closed-door meeting with Mr Lavrov, as well as the Russian ambassador in Washington, Mr Sergei Kislyak.

The Lavrov meeting came just hours after Mr Trump fired his FBI director James Comey, the man responsible for investigating allegations of collusion between the Republican leader's team and Russia.

The embarrassment was compounded by the presence of Mr Kislyak, who is at the centre of a series of questions about contacts between Mr Trump's inner circle and the Russian government.

Mr Comey's shock dismissal ignited furore among Democrats, who suggested that the FBI's investigation into Mr Trump's campaign and Russia could now be tainted, an idea the White House has rejected.

Shortly before his call for peace Mr Trump sent another Twitter missive: "Russia must be laughing up their sleeves watching as the US tears itself apart over a Democrat EXCUSE for losing the election."