LONDON, Nov. 24 (Xinhua) -- The leader of the Northern Ireland's Democratic Unionist Party (DUP) told its annual conference in Belfast Saturday that the party remained opposed to British Prime Minister Theresa May's Brexit deal.

Arlene Foster was speaking as May headed to Brussels ahead of the expected signing of an agreement Sunday between Britain and the European Union (EU) on a future relationship after Brexit.

May's minority Conservative government at Westminster relies on the support of the 10 DUP MPs to give it a majority in the House of Commons. The loss of those vital 10 votes will cause a major headache for May when the deal is debated by MPs next month.

Addressing the conference, Foster said the DUP could not support a Brexit deal that would open the possibility of divergence in either customs or regulatory measures between the British mainland and Northern Ireland.

Foster told the conference the Brexit deal was not in the national interest and would cause long-term economic damage to Northern Ireland.

As part of the deal, a so-called backstop arrangement has been included that could see an option of Northern Ireland keeping some EU customs regulations for a short time after the end of an implementation period due to end in December 2020. It would mean different rules applying in mainland Britain and Northern Ireland, though May insists it will not be used.

The backstop would only be needed if a solution has not been agreed to avoid a hard border between Northern Ireland and the Irish Republic.

Ahead of the conference, Foster warned May she risks losing the support of the DUP support if she presses ahead with her current Brexit deal.

In a media interview in Belfast, Foster called on the Prime Minister to ditch the UK-EU Withdrawal Agreement or face the end of the Westminster pact between the DUP and the Conservatives.

Foster told Radio Ulster's Inside Politics if the deal is not going to deliver on Brexit, the DUP would have to look at the confidence and supply agreement between the two parties.

In a speech at the DUP conference Saturday, former Foreign Secretary Boris Johnson told delegates Britain is on the verge of making a historic mistake if it does not scrap the backstop. It could risk tearing apart the fabric of the United Kingdom, Johnson warned.

He said Northern Ireland faced being reduced to the status of a semi-colony of the EU if the Brexit deal is ratified by the British parliament.

He called DUP MPs at Westminster to work with him and the many Conservative backbenchers who have pledged to vote down May's deal next month.

In what the Daily Telegraph described as a rousing speech to the DUP conference, Johnson said the draft Brexit withdrawal agreement conjured up images of famous ocean liner Titanic heading off to sea, adding: "now is the time to point out the iceberg ahead."

The ill-fated Titanic was built in Belfast and sank on its maiden voyage across the Atlantic in 1912.