EU to publish the first draft of Brexit treaty
The European Union is set to publish a legal draft of its Brexit withdrawal agreement for the first time, detailing the terms of the UK's departure.
The draft document is expected to say Northern Ireland would have to follow EU single market rules to avoid a "hard border", if alternatives are not found.
Downing Street has dismissed any prospect of a return to a hard border.
The prime minister's coalition ally in Northern Ireland has threatened to withdraw support over the issue.
The Democratic Unionist Party said details of the draft treaty "fundamentally breached" an agreement reached in Brussels late last year.
"If the EU or Dublin believes the UK government will be signing up to a border in the Irish Sea, they are deluded," said senior DUP member Sir Jeffrey Donaldson
Mr Donaldson argued the draft divorce treaty would also undermine the constitutional status of Northern Ireland in the Belfast Agreement.
That 1998 treaty - also known as the Good Friday Agreement - between the British and Irish governments and most political parties in Northern Ireland decided how the region would be governed and brought an end to 30 years of sectarian conflict.
The EU commissioners' 120-page draft Brexit withdrawal document will refer to three possible options for avoiding physical infrastructure on the Irish border.
However, the only one to be fleshed out will be the government's least-favourite: the option of Northern Ireland staying within the EU customs union and aligned with European rules and regulations, says BBC Brussels reporter Adam Fleming.