The leaders of the Senate Intelligence Committee said the panel will investigate allegations Russia used cyber attacks to influence the US presidential election, including any links between Russia and the political campaigns.
The committee plans to interview senior officials of both the Trump and Obama administrations and may issue subpoenas to compel testimony, the panel's Republican chairman, Richard Burr, and its top Democrat, Mark Warner, said in a statement.
Donald Trump's pick to lead the Pentagon put Russia at the top of a list of threats to US interests told Congress that America must be ready to confront Moscow where necessary, even as he backed Trump's bid for better relations.
The remarks by retired Marine General James Mattis were the latest by one of Trump's Cabinet picks that veered away from the president-elect's campaign rhetoric, which included praise for Russian President Vladimir Putin and pledges to improve ties with him.
Mattis said Russia, China and Islamist militants were presenting the biggest challenge to the US-led world order since World War Two, and called for Congress to lift spending caps undermining military readiness.
"I'm all for engagement but we also have to recognise reality in what Russia is up to," Mattis said, adding there were a "decreasing number of areas" where the United States might cooperate with Moscow.
Asked about the main threats to US interests, Mattis said: "I would consider the principle threats to start with Russia."
Mattis said he wanted to meet with the new Trump national security team to "craft a strategy to confront Russia for what it's done," when questioned about the possibility of new US sanctions.
Due to enter the White House on Januaru 20, Trump acknowledged that Russia likely hacked the Democratic National Committee and emails of top Democrats during the 2016 presidential election campaign, a conclusion reached by US spy agencies.
