"The prime minister thanks Boris for his work".
He added that plans to create a common rulebook for goods and agrifoods "will make it much more hard to do free trade deals" - a key goal of the Brexit supporters.
Therefore, in the interests of our country and the future of the Conservative Party, I feel the time has come for a new leader and so I am writing this letter to inform you that I have no confidence in the Prime Minister.
Foreign Secretary Boris Johnson and Brexit Secretary David Davis both quit the government this week in protest.
The EU issued a veiled warning that it would not budge on its red lines on Thursday as Theresa May unveiled her long-awaited Brexit plan.More news: Stormy Daniels's strip club charges are dropped hours after arrest
"If they do a deal like that, we would be dealing with the European Union instead of dealing with the United Kingdom, so it will probably kill the deal", Trump said.
Theresa May's plan has been attacked from all sides - as unworkable and damaging for jobs by business figures - and as tying Britain to European Union market rules without any say over them by hard brexiteers.
May's Cabinet agreed to the plan after a 12-hour meeting Friday, but government unity began to fray within hours.
Brexit-supporting lawmakers were angered by the proposals, saying they would keep Britain tethered to the bloc and unable to change its rules to strike new trade deals around the world.
Davis also said that May's plan "would be a risk at least of delivering a poor outcome".
British and European Union officials are hoping to strike a deal on the terms of Britain´s withdrawal and agree to a plan for future trade ties in time for an European Union summit in October.
The plans are an attempt to meet the demands of businesses, pro-EU voters, Brexit supporters and the European Union, which has warned repeatedly that time is running out.More news: Wimbledon 2018: Serena Williams to face Angelique Kerber in women's final
In response to questions about whether the government is in "meltdown", May's spokesman said "it is not".
Le Figaro, the conservative French broadsheet, says the prime minister has been "destabilised by a pro-Brexit revolt", although the inside editorial points out the "mutiny is far from having been won".
Mrs May said she was "sorry - and a little surprised" by Mr Johnson's move after his apparent support on Friday.
Mr Davis was the first to go, followed by Mr Baker, with Mr Johnson resigning in the afternoon, then Mr Green, and then finally Mr Burns.
Davis insisted he did not want his resignation to become a rallying cry for May's ouster.
"Actually despite all the political movement and challenges in Westminster I think this has been a good week for Brexit. I can´t see more ministers resigning", Simon Usherwood, politics lecturer at the University of Surrey, told AFP. "That's not a tenable position".
Conservative lawmakers also worry that leadership election so close to Brexit - due to take place on 29 March 2019 - would embolden Labour and increase pressure for another election which could delay Brexit.More news: World’s ugliest dog dies weeks after winning title