WASHINGTON (BLOOMBERG) - White House Chief of Staff John Kelly said he became aware of problems with security clearances among President Donald Trump's aides soon after he accepted his job last summer.

He also said that former Staff Secretary Rob Porter resigned Feb 6, the same day as a news report about allegations of domestic violence from two ex-wives, contradicting the White House's previous account that Porter quit the following day.

In a briefing for reporters on Friday (March 2), Kelly presented a new timeline for the Porter episode and conceded that the White House had handled it poorly.

"We didn't cover ourselves in glory in terms of how we handled that Wednesday morning," the day after Kelly now says Porter resigned.

Kelly said he did not offer to resign over his handling of Porter, contrary to reports last month that he had raised the idea with Trump.

"I have absolutely nothing to even consider resigning over," he said on Friday.

Clearance Problems Kelly said that within six weeks of joining the White House last summer "it came to my notice that the kind of things I was used to in DOD in terms of the handling of classified material wasn't up to the standards I had been used to," using an acronym for the Defence Department.

Kelly is a retired Marine general.

He learned then that "a number" of staff didn't have permanent security clearances. Porter was among them, though it remains unclear if Kelly knew that at the time.

The chief of staff didn't move until last month, after Porter resigned, to tighten White House clearance procedures and limit access to classified material for people with interim clearances.

More than 30 aides had their clearances reduced from top secret to secret last week after Kelly's review. The controversy over Kelly's handling of Porter and security clearance procedures has shaken confidence in Kelly within the White House and led to speculation he might depart his job.

Porter was among the Trump aides working on an interim clearance, and the White House initially said his background check had not been completed before he quit. But FBI director Chris Wray has said his agency submitted some information on Porter to the White House in March of 2017, a full background report in July, and followed up with additional information in November and earlier this year.

There was a "disconnect" at the White House, Kelly said. "When that got looked at, I do not know, but Chris Wray was right and it was a shock for me, certainly, because I thought the information that came over was in November."

The Daily Mail Online, a US website owned by a British tabloid, published an interview with Porter's second wife in which she alleged mainly emotional and verbal abuse at about 7pm on Feb 6. Kelly said that after the Daily Mail contacted the White House at about 5pm that evening, he spoke to Porter about the report and he denied it.

Kelly went to an immigration meeting at the Capitol that evening. When he returned to the White House, a subsequent press inquiry arrived at about 7.30pm alleging Porter had physically abused his first ex-wife, he said.

"I talked to Rob and he just, he resigned," Kelly said.

Early on Feb 7, the Intercept published an interview with Porter's first wife, including a photo of a black eye she said he had inflicted.

Kelly said he instructed aides to allow Porter back in the White House on Feb 7 only long enough to close out his work, and he believed Porter told his subordinates that evening that he had resigned.

"The mix-up came I guess the next day," Kelly said.

White House Press Secretary Sarah Huckabee Sanders told reporters at about 1.30pm on Feb 7 that Trump and Kelly retained "full confidence and trust" in Porter. She then issued a statement from Porter calling the allegations "outrageous" and "simply false." She said he had resigned, but that "it won't be immediate" and that his departure was "a personal decision that Rob made."

The White House issued a statement from Kelly complimenting Porter as a "a man of true integrity and honour" that made no mention of the allegations against him.

In the evening, Kelly issued a new statement condemning domestic violence. The following day, Feb 8, was Porter's last day in the office, Deputy Press Secretary Raj Shah told reporters at the time.