Theresa May is meeting European leaders and EU officials on Tuesday for talks aimed at rescuing her Brexit deal, the BBC reports.
She is holding talks with Dutch PM Mark Rutte and Germany's Angela Merkel after postponing a Commons vote on the deal.
The UK PM has said she needs "further assurances" about the Northern Ireland border plan to get backing from MPs.
European Commission President Jean-Claude Juncker said the EU would not "renegotiate" the deal but there was room for "further clarifications".
The prime minister is understood to be seeking legal guarantees that the UK will not be trapped in the Northern Ireland backstop plan indefinitely.
MPs have to give the go-ahead for Mrs May's deal if it is to come into effect when the UK leaves the EU on 29 March.
The European Court of Justice ruled on Monday that the UK can cancel Brexit without the permission of the other 27 EU members.
The ECJ judges ruled this could be done without altering the terms of Britain's membership.