Two top Senate Democrats have called for a federal investigation into Elon Musk's reported contacts with Russian President Vladimir Putin and his top aides.

The senators have urged the Pentagon and the Justice Department to determine whether the conversations, which the Kremlin has denied, should force a review of the federal government's contracts with Musk's company, SpaceX.

The Wall Street Journal reported last month that the world's richest person has had "multiple, high level conversations" with Putin since 2022 while also sustaining contact with other top Russian officials.

Musk wrote on his X platform on Friday that he's "going to find out who's making these accusations and nuke them".

In another post, he slammed the two Democrats - Rhode Island Senator Jack Reed, chairman of the Senate Armed Services Committee, and New Hampshire Senator Jeanne Shaheen, a senior Democrat on the Armed Services and Foreign Relations Committees - as "puppets" and "knuckleheads".

The pair of Democrats sent a letter on Friday to Attorney General Merrick Garland and Defence Department Inspector General Robert Storch raising "serious questions regarding Mr Musk?s reliability as a government contractor and a [security] clearance holder".

The Donald Trump ally currently benefits from billions of dollars in US defence and intelligence contracts, and also claims to hold a top secret level security clearance.

"Russia?s ambitions in the space domain pose a direct threat to US national security," Reed and Shaheen write, pointing to reports earlier this year that the US adversary has deployed a counter-space weapon that may be capable of attacking other satellites in low-earth orbit.

The senators note that, unlike others with high-level security clearance, Musk does not report his contacts with foreign government officials.

They add that the billionaire's communications with Putin's deputy chief of staff, Sergei Kiriyenko, comes amid a Justice Department finding that Kiriyenko and other top officials were involved in an effort to seed Kremlin propaganda on social media, including on the Musk-owned X (formerly Twitter) platform.

"For these reasons, we urge an immediate review to ascertain whether Mr Musk?s relationship with multiple high-level Russian officials warrant an investigation and a determination by the Department of Defense?s senior debarment official whether SpaceX should exclude Mr Musk?s involvement in current or future US Government contracts," Reed and Shaheen write.

Musk, who backed Trump's successful 2024 re-election bid with campaign appearances and millions of dollars in donations, was picked by the president-elect earlier this week to lead a new "Department of Government Efficiency".

But he has also participated in the incoming president's diplomatic efforts.

Musk joined phone calls over the past week with Ukrainian President Volodymyr Zelensky and Turkish President Tayyip Erdogan.

The BBC's US partner, CBS News, reported on Friday that he also recently visited the residence of Iran's United Nations ambassador in New York. Washington does not have diplomatic relations with Tehran. (BBC)

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