WASHINGTON - The confirmation of Kathleen Troia "K.T." McFarland as US Ambassador to Singapore may be in limbo, reflecting a degree of turmoil in Washington triggered by the FBI's investigation of President Donald Trump campaign's potential collusion with Russia during last year's US presidential election.

The nomination confirmation was stalled after Ms McFarland appeared to contradict her statements about her knowledge of any communications between Russia's then Ambassador in Washington, and Mr Michael Flynn, a key Trump campaigner later appointed national security adviser in the administration.

She had told the Senate Foreign Relations Committee in written comments for her confirmation hearing in September that she "was not aware" of any communications between the two men. But the New York Times reported on Monday that it had obtained an e-mail Ms McFarland sent on Dec 29, 2016, the day former President Barack Obama's administration authorised new sanctions against Russia, saying Mr Flynn would talk to Mr Kislyak that evening.

Mr Flynn, a former lieutenant-general, pleaded guilty on Friday to lying to the Federal Bureau of Investigation about his contacts with Russia, and agreed to cooperate with prosecutors delving into the actions of President Trump's inner circle before he took office.

Maryland Senator Ben Cardin, the top Democrat on the Senate Foreign Relations Committee, told CNN: "I think there should be no action on this nomination until we get the information."

Ms McFarland's appointment was due to go to a vote in the full Senate. It is unclear what will happen to her nomination now. Reuters reported that Senate Majority Leader Mitch McConnell would have to take procedural steps in order to overcome the hold and confirm her nomination, which would eat up valuable floor time in the Senate.

"It looks like a fraught nomination," Ernie Bower, CEO of consultancy BowerGroupAsia, told The Straits Times.

This may leave the US without an ambassador in Singapore for the foreseeable future.

Mr Bower said: "It is hard not to have an ambassador in the country chairing Asean". The US has also not nominated an ambassador to Asean either, he noted.

The majority of US ambassadors posted abroad are career State Department officials, but about 30 per cent of them have been political appointees in recent years, especially to countries with which Washington has significant ties. US ambassadors to Singapore have been political appointees for the past three decades, since veteran diplomat J. Stapleton Roy left in 1986. When Bill Clinton took office in 1993, there was no US ambassador to Singapore for over a year.

Delays in appointments to key posts abroad have raised eyebrows in Washington. The US Ambassador to Seoul, said to be seasoned Korea hand Dr Victor Cha, has not been nominated either. Analysts see the State Department as somewhat been marginalised, with the White House running foreign policy directly. Mr Trump last week said that Secretary of State Rex Tillerson was still on board the administration, following speculation in the US media that the secretary was on the verge of being replaced.

This is not the longest time the US embassy in Singapore has been without an ambassador. According to the US embassy website, after Patricia Herbold left the post in Jan 2009, it took more than a year for the next ambassador to be appointed.

Ms McFarland served as Deputy National Security Adviser to Mr Flynn before he was fired in February, after it was revealed that he had misled Vice-President Mike Pence over the nature of his contacts with the Russian Ambassador.

At issue in the Flynn case is a call between him and Russian Ambassador Kislyak on Dec 29, 2016, in which he apparently urged Moscow not to react harshly to sanctions imposed by President Barack Obama following US intelligence assessments that Russia had interfered in the presidential election.

Months later, President Trump fired FBI director James Comey, who later testified before the Senate that the President had asked him to go easy on investigating Mr Flynn's contacts with Russia.

Mr Trump has called the Russia investigation a witch hunt designed to discredit his election win. He has maintained that Mr Flynn was merely doing his job when he spoke with foreign ambassadors.

On Monday he told reporters: "I feel badly for General Flynn. I feel very badly.

"Hillary Clinton lied many times to the FBI and nothing happened to her. Flynn lied and they destroyed his life, I think it's a shame."

Ms McFarland, a 65-year-old mother of five grown-up children, had her appointment as ambassador to Singapore endorsed by among others, Cold War veteran Henry Kissinger.

She began her career in the 1970s as a night shift secretary on Mr Kissinger's staff. She went on to work for three US Presidents - Richard Nixon, Gerald Ford and Ronald Reagan - on the National Security Council, in the Department of Defence, and in the administration. She was also a regular contributor to Fox News on security issues.

Ms McFarland is widely seen as having President Trump's ear. In May a senior Washington diplomat told The Straits Times: "She understands the President; she would be able to articulate his strategic world view."

In the Reagan administration, Ms McFarland worked as a speech writer to then Defence Secretary Caspar Weinberger, whose 1984 Weinberger Doctrine laid out guidelines for circumstances under which the US should become involved in military operations overseas - and is echoed in the Trump administration's "peace through strength" approach.

At a Jan 10 conference on America's role in the world at the US Institute for Peace in Washington, she told the audience: "We have a President who is going to seize this unique historic moment (and) is going to rebuild America's defences."

American values would "continue to be the bedrock, American global leadership is going to continue", she said.