President Donald Trump is evaluating U.S. national security adviser Michael Flynn over his Russian contacts, Trump's spokesman said on Monday, pointedly declining to make a public show of support for his embattled aide.

A statement from White House press secretary Sean Spicer, read to reporters crowded around his office, left Flynn's status in doubt, an hour after Trump aide Kellyanne Conway said the president had full confidence in Flynn.

Flynn had told Vice President Mike Pence he had not discussed U.S. sanctions against Russia with Russian officials in the weeks before Trump took office Jan. 20, prompting Pence to defend him in subsequent television interviews.

In recent days Flynn has acknowledged he might have discussed sanctions with the Russians but could not remember with 100 percent certainty, which officials said had upset Pence, who felt he had been misled.

Officials said Flynn has apologized to Pence twice, including in person on Friday.

"The president is evaluating the situation. He is speaking to ... Vice President Pence relative to the conversation the vice president had with General Flynn and also speaking to various other people about what he considers the single most important subject there is, our national security," Spicer said.

Flynn was an early supporter of Trump and shares his interest in shaking up the establishment in Washington.

The White House statement, arranged during a meeting between Trump, White House chief of staff Reince Priebus and Spicer, suggested that the review into Flynn's activities stretched beyond the conversations he had with Russian officials.

Some news reports have focused on accusations that there has been dysfunction in the operation of the National Security Council with Flynn at the helm.

An hour before Spicer read his statement, Conway, one of Trump's closest aides, had told reporters that Flynn had the full confidence of the president.

It was notable, however, that Trump did not use the opportunity of a joint news conference with visiting Canadian Prime Minister Justin Trudeau on Monday to make a public show of support for Flynn.

Top White House officials have been reviewing Flynn's contacts with the Russians and whether he discussed the possibility of lifting U.S. sanctions on Russia once Trump took office.

That would potentially be in violation of a law banning private citizens from engaging in foreign policy, known as the Logan Act.

Senate Democratic leader Charles Schumer told reporters he wanted an independent investigation of Flynn’s discussions with the Russians.

“His security clearance ought to be withdrawn until that independent investigation is completed. And if he has violated any law or ethical precept, he ought to be fired," Schumer said.

There was no indication from transcripts of Flynn’s conversations that he had promised to lift the sanctions but rather that he made more general comments about hoping for better U.S.-Russian relations with Trump, a U.S. official said.

Flynn was going about his business as normal despite the cloud hanging over him, participating in national security meetings.

He was at Trump's side at the president's Mar-a-Lago retreat in Florida on Saturday when word reached the presidential entourage that North Korea had launched a ballistic missile at the same time Trump was hosting Japanese Prime Minister Shinzo Abe.

While Trump left Flynn's status pending, he appeared to close the door on another source of speculation, as to whether Priebus might be replaced.

Appearing briefly before reporters in the West Wing of the White House, Trump said Priebus was doing a "great job."