Johnson on Sunday said women who wear burqas "look like letter boxes" and compared them to "bank robbers".
Johnson resigned as Foreign Secretary in July, accusing Theresa May of killing "the Brexit dream" with her plan to seek close economic ties with the European Union after the United Kingdom leaves the bloc next year.
"These were offensive comments but clever politics", she said.
"Johnson did not go far enough".More news: Breast-Feeding Tips For New Moms..
"I also believe Dominic speaks for many millions of people who despair at the state of both main parties".
"If you say that it is weird and bullying to expect women to cover their faces, then I totally agree - and I would add that I can find no scriptural authority for the practice in the Koran".
However, as Britain's departure from the European Union pans out in coming months, the next leadership contest will be seen within the party through the prism of Brexit. "I don't regard him as a fit and proper person to lead a political party and certainly not the Conservative party", he said.More news: NCAA basketball changes: Undrafted players can return to school
Mohammed Sheikh, founder of the Conservative Muslim Forum, said Johnson's article had been "totally out of order". "If we need to take the whip off, let's do it", he told Sky News.
In other words, the former Foreign Secretary is ready to ride the same populist wave that delivered the vote for Brexit two years ago.
Mr Johnson stirred up a hornet's nest after he made the comparison in a column in The Daily Telegraph.
"It is any wonder that many younger women have internalised this poisonous chauvinism by asserting that it is their human right to hide their faces? He should not have used it", May said.More news: Kanye's 'Carpool Karaoke' cancelations have cost James Corden $45K