Northern Ireland's Democratic Unionist Party (DUP) said today it would support Prime Minister Theresa May's government on legislation concerning Britain's exit from the European Union, securing her a slender majority in parliament.

May struck a deal with the DUP today to back her administration after she failed to secure an outright victory in a botched June 8 snap election.

"The DUP... agrees to support the government on legislation pertaining to the United Kingdom's exit from the European Union; and legislation pertaining to national security," a document published by May's office said.

The DUP also agreed to support the British government in parliamentary votes on the budget, and on all Brexit and national security legislation, Prime Minister Theresa May said later.

May also urged Northern Irish political parties to agree over the province's government by a June 29 deadline.

"The DUP will support the Conservative government on votes on the Queen's Speech, the Budget, and legislation relating to Brexit and national security," May said.

"The agreement makes clear that we remain steadfast to our commitments as set out in the Belfast Agreement and its successors, and in governing in the interests of all parts of the community in Northern Ireland," she added.