"The (Republican) majority was not interested in conducting any further investigation, even when the flaws in what we have done so far have become so apparent in the course of the last week," Schiff said.

Reports have emerged from a whistleblower this week that British political consultancy Cambridge Analytica improperly accessed Facebook Inc users' information to build profiles on American voters later used to help elect Trump in 2016.

Hidden camera footage released by British television showed a company official criticizing how the House committee had conducted its interview.

President Donald Trump's fellow Republicans have majorities in both the Senate and House, controlling every congressional committee. The House panel's investigation of how Russia might have sought to influence the 2016 US presidential election, and whether Trump associates colluded with Moscow has, has been marked by partisan disagreements for months.

Republicans announced two weeks ago that the panel's investigation was over and they had found no evidence of collusion between Trump's campaign and Russian efforts to influence the vote, a conclusion rejected by Democrats, who pledged to continue investigating.