A retired Cambridge professor suspected of being an FBI source in the Russia investigation was later recommended for a US ambassadorship in the Trump administration, claims reports.

Prof Stefan Halper, 73, has emerged as a key figure in a battle playing out between Donald Trump and his own justice department.

According to reports, the professor approached the Trump campaign aides in the summer of 2016 in an attempt to glean information about any collusion with Russia for an FBI operation, code-named Crossfire Hurricane.

The American professor, who is a Life Fellow of Magdalene College, has not commented on the reports. The FBI declined to comment.

Republicans in Congress have been pushing for more details of the investigation and the role of the suspected informant.