Michael Flynn, President Donald Trump's first National Security Advisor who unceremoniously resigned over allegations he had spoken to the Russian ambassador before taking public office, has offered to testify to officials investigating alleged links between the Trump campaign and Russia in exchange for immunity, sources have told the Wall Street Journal (WSJ).

Flynn's lawyer told the Associated Press (AP) that the former general was in talks with congressional panels and seeking to avoid "unfair prosecution". The WSJ cited "officials with knowledge of the matter".

The reports said that Flynn had made the offer to intelligence committees in the House of Representatives and the Senate, as well as the FBI, but none had so far taken him up.

The scandal that enveloped Flynn and led to his ejection from the White House centred around calls that he took from the Russian ambassador before taking public office.

During the calls, he allegedly discussed lifting Obama-era sanctions on Russia, thereby potentially breaking a US law which states that private individuals are prohibited from engaging in foreign policy.

Flynn was also said to have misled Vice President Mike Pence over the calls, leading him to publicly defend Flynn while not being fully briefed on the situation.

In his resignation letter, Flynn said that he had "inadvertently briefed the Vice President Elect and others with incomplete information regarding my phone calls with the Russian ambassador".

Flynn's reported quest for immunity casts a new shadow over the Trump campaign's rejection of allegations that members colluded with Russian officials.

This week the Senate Intelligence Committee started hearing public testimony in their investigation into Russia's alleged interference in the US presidential election.

Meanwhile, over in the House of Representatives the House Intelligence Committee has faced further calls for its chairman, Devin Nunes, to resign after allegations that he is too close to the White House to conduct the investigation.