(CNN) The House Intelligence Committee plans to hold two off-site interviews next week with high-profile witnesses who have ties to President Donald Trump, prompting grumbling among Democrats who contend that the GOP is rushing to wrap up the Russia probe, with more left to investigate.

The witnesses -- one is a Russian-American businessman, Felix Sater, and the other Trump's longtime personal assistant, Rhona Graff -- will be interviewed by Republican and Democratic staff next week in New York, two sources said. That could prevent lawmakers from interviewing the witnesses if they have to stay in town to vote on Capitol Hill, leaving the matter to committee staff.

The New York interviews were first reported by The Wall Street Journal , which cited a Republican source who said the decision to conduct the interview in New York was to accommodate one of the witnesses' lawyers, who was injured.

It comes as a third witness, Alexander Nix of the data firm Cambridge Analytica, testified via videoconference before the House panel on Thursday, according to two sources familiar with the matter. Nix told the House panel that he did not discuss Russia with the Trump campaign, one of the sources said.

Democrats complain that the panel is moving at a pace that has prevented them from fully vetting the witnesses, chasing new leads or receiving documents far enough in advance to prepare adequately to question the witnesses.

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