LONDON (Reuters) - There are significant outstanding issues in Brexit negotiations over the Irish backstop and work is ongoing to resolve them, British Prime Minister Theresa May’s spokesman said on Monday.

Irish Prime Minister Leo Varadkar said on Monday Ireland was willing to examine ways in which a backstop to keep the Irish border open after Brexit could be reviewed, so long as Britain could not unilaterally walk away from it.

“We have made good progress but clearly in relation to the backstop there are outstanding and significant issues. In terms of resolving those, those talks are ongoing,” the spokesman said.