US President Donald Trump dodges question on whether he has worked for Russia

US President Donald Trump avoided giving a direct answer when asked if he currently is or has ever worked for Russia after a published report said federal law enforcement officials were so concerned about his behaviour after he fired James Comey from the FBI that they began investigating whether Trump had been working for the US adversary against American interests.

Trump said it was the "most insulting" question he'd ever been asked.

The New York Times report on Friday cited unnamed former law enforcement officials and others familiar with the investigation.

It has been reported that the FBI became suspicious of Trump's ties to Russia during the 2016 presidential campaign. Photo / Getty

Trump responded to the report on Saturday during a telephone interview broadcast on Fox News Channel after host Jeanine Pirro, who is also a personal friend of the president, asked whether he is currently or has ever worked for Russia.

"I think it's the most insulting thing I've ever been asked," Trump said. "I think it's the most insulting article I've ever had written, and if you read the article you'll see that they found absolutely nothing."

Trump never answered Pirro's question directly, but went on to say that no president has taken a harder stance against Russia than he has.

"If you ask the folks in Russia, I've been tougher on Russia than anybody else, any other ... probably any other president, period, but certainly the last three or four presidents."

The Times reported that FBI agents and some top officials became suspicious of Trump's ties to Russia during the 2016 presidential campaign but didn't open an investigation at that time because they weren't sure how to approach such a sensitive and important probe, according to the unnamed officials. But Trump's behaviour in the days around Comey's May 2017 firing as FBI director, specifically two instances in which he seemed to tie Comey's ousting to the Russia investigation, helped trigger the counterintelligence part of the investigation, according to the newspaper.

A protester with a poster of Trump and Putin outside the Phoenix Convention Center where Trump was holding a rally in August 2017. An FBI investigation was launched in May 2017. Photo / Getty

In the inquiry, counterintelligence investigators sought to evaluate whether Trump was a potential threat to national security. They also sought to determine whether Trump was deliberately working for Russia or had unintentionally been influenced by Moscow.

Trump tweeted early Saturday that the report showed that the FBI leadership "opened up an investigation on me, for no reason & with no proof" after he had fired Comey.

Robert Mueller took over the investigation when he was appointed special counsel soon after Comey's firing. The overall investigation is looking into Russian election interference and whether Trump's campaign coordinated with the Russians, as well as possible obstruction of justice by Trump. The Times says it's unclear whether Mueller is still pursuing the counterintelligence angle.

Trump's lawyer Rudy Giuliani told the Times he had no knowledge of the inquiry but said that since it was opened a year and a half ago and they hadn't heard anything, apparently "they found nothing."

Trump has also repeatedly and vociferously denied collusion with the Russians.

- AP