WASHINGTON (AFP) - President Donald Trump again took aim on Saturday (Dec 23) at deputy FBI director Andrew McCabe, saying he was "racing the clock to retire", as US media reported Mr McCabe plans to step down.

"FBI Deputy Director Andrew McCabe is racing the clock to retire with full benefits," Mr Trump tweeted. "90 days to go?!!!"

CNN, CBS and The Washington Post all reported that the 49-year-old Mr McCabe plans to retire, possibly in March, when he will be eligible for full pension benefits. An FBI spokeswoman did not immediately respond to a request for comment.

Mr McCabe has faced intense pressure from Mr Trump, who for more than a year has challenged the FBI official's connections to the Democratic Party even while suggesting more recently that the long-respected agency was "in tatters".

But with administration officials themselves under mounting pressure from the investigation by former FBI chief Robert Mueller into links between Mr Trump's election campaign and Russia, the president's pointed criticism of Mr McCabe has raised concerns among Democrats who fear he might be laying the groundwork to oust, or at least undermine, Mr Mueller.

In a second tweet on Saturday, Mr Trump suggested that Mr McCabe's wife, a Virginia politician, had been given US$700,000 (S$940,800) by allies of Mrs Hillary Clinton at a time he was involved in the investigation into Mrs Clinton's use of a private e-mail server.

The FBI has said Mr McCabe did not start overseeing the Clinton investigation until his wife's campaign for the Virginia Senate was over.

A Justice Department inspector general has been examining Mr McCabe's role in the Clinton investigation.

Democrats have urged Mr McCabe to resist pressure to step down, which they say is politically motivated.