Countering strident attacks on his agency from the president who appointed him, Christopher Wray, the FBI director, on Thursday defended the tens of thousands of people who work with him and declared: "There is no finer institution."

Mr Wray, who has led the agency for just four months, fended off politically charged questions from politicians of both parties during a routine oversight hearing that was overtaken by questions about Hillary Clinton's emails and President Donald Trump's campaign.

Citing pending investigations, he repeatedly declined to answer questions about either, while also refusing to give an opinion on whether Mr Trump could be accused of obstructing justice.

But he did not hesitate to defend the nation's premier law enforcement agency following a weekend of Twitter attacks by Mr Trump, who called the FBI a biased institution whose reputation was "in Tatters — worst in History!" and urged Mr Wray to "clean house".

The outburst from the president followed a guilty plea from his former national security adviser for lying to the FBI and the revelation that an agent had been removed from a special team investigating the Trump campaign because of text messages seen as potentially anti-Trump.