A Russian artist who painted a portrait of Donald Trump that was given to the US president by Vladimir Putin says he never suspected his work would become an instrument of Russia-US diplomacy.

The painting by Nikas Safronov depicts Trump clenching his fist in a gesture of defiance in the moments after a gunman tried to assassinate him at a rally in Pennsylvania last July.

Safronov told Reuters he was impressed by Trump's courage. "I went to a nearby church and prayed for him. And then I started to make sketches," he said.

But the portrait's unlikely journey to the White House via the Kremlin came as a surprise, Safronov added. He said he was approached by former clients, whom he did not name, who requested that he give them the painting for a period of time.

Safronov said he agreed and gave it away for free. Later, he said, he heard media reports that Trump's special envoy Steve Witkoff had said that Putin had gifted Trump a painting by a famous Russian artist.

"Somehow I couldn’t piece together that those people (who took away the portrait) work for the president of Russia," he said.

Witkoff, who has met Putin four times, said in March that he had brought back the painting, which he said Putin had commissioned from a leading Russian artist, and Trump had been "clearly touched" by it.

But Safronov said he only realised that the portrait given to Trump was his when he received a call from Putin.

"The president called me. He thanked me and said he liked the work. It was a short conversation," he said.

He now hopes it will help foster a breakthrough between the two countries, which since Trump's return to the White House in January have launched diplomatic contacts on ending the war in Ukraine and repairing bilateral relations.

"I hope it will play its role and bring peace to the world," said Safronov.