US President Donald Trump and Russian leader Vladimir Putin had a "very robust and lengthy exchange" on allegations of Moscow's meddling in US elections, Secretary of State Rex Tillerson said Friday. 

During Trump and Putin's first face-to-face talks, the US property tycoon pressed the ex-KGB agent "on more than one occasion" on the claims, said Tillerson, who was in the meeting. Putin denied any such involvement, he added.