A former senior FBI agent fired over his critical text messages about US President Donald Trump filed a lawsuit on Tuesday against his former employer.

Peter Strzok accuses the FBI of violating his privacy by sharing the text messages with journalists.

"The campaign to publicly vilify Special Agent Strzok contributed to the FBI's ultimate decision to unlawfully terminate him," the suit says.

Strzok was removed from a special probe into links between Trump's 2016 presidential campaign and Russia after the Justice Department's inspector general found the messages. He was fired from the FBI in August 2018.

Using his FBI phone, Strzok sent text messages disparaging Trump as a presidential candidate to FBI lawyer Lisa Page. Strzok and Page were having an affair at the time.

'Unrelenting pressure'

After the messages went public, Trump and his supporters cited them as indicative of an anti-Trump bias within the FBI.

Strzok's lawsuit alleges that "unrelenting pressure from President Trump and his political allies in Congress and the media" caused the FBI deputy director to ignore a disciplinary recommendation to demote and suspend Strzok rather than fire him.

He also says that the government acted unfairly because it had "consistently tolerated and even encouraged" pro-Trump "political speech" by other officials.

Strzok is seeking to be reinstated, receive back pay and get an official declaration that the government violated his constitutional rights.

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