Devin Nunes, the Republican chairman of the US congressional committee on intelligence, said on Sunday: "Everything I have up to this morning - no evidence of collusion." 

Nunes' committee is investigating whether the Trump campaign and the Russian government worked together to boost the real-estate magnate's chances of winning the US presidency.

US intelligence agencies have accused Moscow of hacking computer systems belonging to Hillary Clinton's Democratic Party, among other methods.

Moscow has flatly denied the allegations, while Trump has described claims linking his team with the hacking probe as a "total witch hunt."

Hacking, leaks, wiretaps

As well as investigating the extent of communications between the two parties in the lead-up to the November 8 election, the committee is also probing alleged leaks to US media about Trump aides caught up in the scandal.

Nunes told US broadcaster Fox News that a leak relating to Trump's former national security adviser Michael Flynn was a crime, adding that the panel was probing whether other names had been disclosed.

Flynn, a former US army lieutenant general, resigned barely three weeks into the job, after misleading lawmakers about his talks with Russian diplomats before taking up the position.

He is one of several of Trump's associates alleged to have held private talks with officials in Moscow.

Repeated contacts

"The New York Times" reported in February that US intelligence agents had intercepted calls showing repeated contacts between Trump's team and top Russian intelligence officials in the year preceding the US vote.

Adding to the intrigue, Trump's Attorney General Jeff Sessions has removed himself from any Russia-related investigations after it was learned that he had met twice with the Russian ambassador in the months before Trump took office.

Meanwhile, Trump has accused the Obama administration of tapping his phones during the election campaign, which several senior officials have denied. On Sunday, Nunes said he saw "no indication" that the wiretapping had taken place.

On Monday, FBI director James Comey is due to appear before Nunes' panel, facing lawmakers seeking answers about the two scandals, which have dominated US politics for several weeks.

Analysts say the hearing is likely to be a very public showdown between the FBI and lawmakers, with the national security world certain to watch whether Comey drops a political bombshell on Washington.

mm/tj (AFP, AP, Reuters)