The top Democratic lawmaker on the US Senate Intelligence Committee says the panel will ask President Donald Trump’s oldest son and son-in-law to provide additional documents as part of the investigation into potential ties between Trump’s election campaign and Russia.

Virginia Senator Mark Warner said Thursday the committee requested the documents "as recently as this week," after Donald Trump Jr. released emails in which he appeared eager to accept Russian government information that could damage the campaign of Hillary Clinton, Trump’s Democratic presidential rival last year.

Warner has said he wants Trump Jr. and Trump's son-in-law, Jared Kushner, to testify at the intelligence committee. “It’s very important that we have all of the appropriate information so we can ask the right questions," he added.

Warner said earlier this week that emails published by Trump Jr. showed "black and white" that the Trump campaign was involved in Russian efforts to influence the presidential election.

Senate Intelligence Committee Chairman Richard Burr would not say Thursday when he wanted to speak with Kushner or Trump Jr.

The FBI as well as several congressional committees are investigating whether the Russian government coordinated with Trump associates during the 2016 campaign and transition.

On Tuesday, Trump Jr. posted a series of emails between himself and Rob Goldstone, a music publicist about an opportunity to receive potentially damaging information about Clinton as part of a Russian government effort to help his father win the election.

The information “would incriminate Hillary and her dealings with Russia and would be very useful to your father,” reads one of the emails.

The US intelligence community has accused Russia of running a series of high-profile cyber attacks to change the outcome of the November 8 presidential election. Russian President Vladimir Putin has firmly denied the hacking allegations.

Trump has repeatedly rejected such reports and has expressed support for improving relations with the US’ former Cold War foe.