British Prime Minister Theresa May will meet with Scotland's leader Monday for the first time since they faced off in a struggle over a new push for Scottish independence as the U.K. leaves the European Union.

May was due to hold talks with First Minister Nicola Sturgeon, days after Sturgeon demanded a referendum on Scottish independence to be held within two years.

May's London-based government must approve a legally binding referendum, and May says "now is not the time" for a new independence vote.

In a 2014 referendum, Scots voted by 55 percent to 45 percent to remain part of the United Kingdom. At the time, Sturgeon's Scottish National Party said it was a once-in-a-generation choice. But Sturgeon now says Britain's looming departure has transformed the situation.

On Tuesday, Scotland's Edinburgh-based parliament is due to vote on a motion formally authorizing Sturgeon to seek a new referendum.

May is touring the U.K. before triggering the EU exit process, trying to shore up support for Britain's exit from the bloc. On Wednesday, she will invoke Article 50 of the EU's key treaty, starting a two-year countdown to Brexit.

In a speech to civil servants at the Department for International Development near Glasgow, May promised stronger powers for Scotland, Wales and Northern Ireland and said she would never allow "our union to become looser and weaker, or our people to drift apart."

"As Britain leaves the European Union, and we forge a new role for ourselves in the world, the strength and stability of our Union will become even more important," she said.