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

The lawmakers have urged the Pentagon and Justice Department to determine whether Musk's alleged relations with a US adversary while holding major government contracts puts national security at risk.

The Wall Street Journal reported last month that the world's richest person has had "multiple, high-level conversations" with Putin since 2022, which the Kremlin has denied.

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

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 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 multi-billionaire claims to hold a top-secret level clearance and his SpaceX company - one of the main contractors to the National Aeronautics and Space Administration (Nasa) - is deeply embedded in the federal government's defence and intelligence infrastructure.

"Russia’s ambitions in the space domain pose a direct threat to US national security," the senators wrote.

Reed and Shaheen noted that, unlike others with high-level security clearance, Musk does not appear to report his contacts with foreign government officials.

They pointed to Musk's alleged communications with Putin's deputy chief of staff, Sergei Kiriyenko.

The Justice Department has said 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 to reducing international support for Ukraine and influence voters in the US presidential election.

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

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

Musk joined Trump's calls over the past week with Ukrainian President Volodymyr Zelensky and Turkish President Tayyip Erdogan, as well as a meeting with Argentinian President Javier Milei at Trump's Florida home.

The BBC's US partner, CBS News, reported on Friday that Musk recently visited the residence of Iran's United Nations ambassador in New York.

It is not clear if Trump or his national security team were aware of the meeting.

Washington does not have diplomatic relations with Tehran and Iran's foreign minister denied on Saturday that any such meeting had taken place.