An EU flag flutters during an anti-Brexit demonstration outside the Houses of Parliament in London, Britain January 28, 2019. REUTERS/Hannah McKay

BRUSSELS (Reuters) - A Brexit deal seemed close on Saturday after the EU indicated legal ways for London to unilaterally leave the contentious Irish border backstop, sources in the bloc said, but the plan was rejected by British Prime Minister Theresa May’s cabinet.

The bloc’s Brexit negotiators on Monday updated envoys of the 27 states staying in the European Union after Brexit on the status of the talks, which have stalled just 18 days before Britain is due to leave on March 29.

May’s parliament is due to hold a new series of votes on Brexit starting on Tuesday but the sides are at loggerheads over the so-called backstop, or an emergency fix aimed at avoiding controls on the sensitive Irish border after Brexit.

“On Saturday evening, it seemed negotiating teams are close to an agreement,” the ambassadors were told, according to a source briefed on the closed-doors meeting.

“But eventually, PM May had failed to convince her cabinet, which she conveyed to European Commission President Jean-Claude Juncker during their phone call on Sunday evening.”

The 27 national EU leaders will discuss Brexit in Brussels on March 21 without May, and should not engage in direct negotiations with the British leader at the two-day summit, the ambassadors were also told.

May could go to Strasbourg, France, on Monday, where the bloc’s executive European Commission and the European Parliament hold sessions this week. But that has not yet been confirmed in London.

May had not ruled out coming up with another UK declaration on the backstop on Monday, according to the briefing the EU ambassadors were given.

Brussels worries that she would ask the House of Commons to vote on backstop solutions that have been rejected by the EU side, which would not make reaching an EU-UK agreement any easier.