A second referendum on Britain's European Union membership has been explicitly ruled out by Prime Minister Theresa May.

Speaking as Cabinet ministers met for the first time after the summer recess, May said the U.K. government has an "opportunity" to rebuild Britain's place in the world after Brexit.

The British public voted by a 52-48 percent margin to leave the EU in a referendum last June, but exit negotiations will not begin until 2017.

"We'll be looking at the next steps that we need to take, and we'll also be looking at the opportunities that are now open to us as we forge a new role for the U.K. in the world," said May, who opposed Brexit before the referendum, as she opened Thursday's meeting.

"We must continue to be very clear that 'Brexit means Brexit,' that we're going to make a success of it.

"That means there's no second referendum; no attempts to sort of stay in the EU by the back door; that we're actually going to deliver on this."

Several opposition figures-including Owen Smith, who is running for leadership of the main opposition Labour Party-have committed to a second referendum on EU membership if they came to power.

May, who became prime minister last month following David Cameron's resignation, created a new ministry-the Department for Exiting the European Union-to coordinate Britain's exit negotiations and appointed David Davis, a prominent critic of the EU, as its secretary of state.

But ministers remain divided over whether Britain will continue to be part of the European single market for trade. Such a step would likely require the U.K. to sign up to EU rules allowing free movement for workers, which is opposed by anti-immigration campaigners.