Britain's prime minister told Northern Ireland politicians on Friday that progress had been made on easing post-Brexit trade rules as he sought to keep the province's skeptical unionists on side in a final push for a deal with the European Union.

After weeks of intense London-Brussels talks, momentum has been building towards a deal to revise the Northern Ireland Protocol - the arrangements agreed to avoid a hard border with EU member Ireland when Britain exited the EU in 2020.

One EU diplomat said it appeared a deal was close and that a meeting in Brussels on Friday between British Foreign Secretary James Cleverly and EU Brexit chief Maros Sefcovic could prepare the ground for a rapid conclusion.

"We have been at this sort of stage before so nobody is ready to uncork the champagne yet," another EU diplomat said.

During an overnight stay at a hotel on the outskirts of Belfast, British Prime Minister Rishi Sunak focused his attention on the Democratic Unionist Party, whose opposition to the protocol must be overcome to make any deal work.

"I will simply say that on some very important issues I think there has been real progress," the DUP's Jeffrey Donaldson, who unlike other political leaders met Sunak late on Thursday as well as on Friday, told reporters afterwards.

"But there remain some outstanding issues that we need to get over the line, and we will then examine the final text of any agreement very carefully."

The DUP have proven to be central players in almost seven years of often tortuous Brexit talks and their resistance has torpedoed previous attempts at agreement. Donaldson said his party would keep working until an outcome meets its red lines.

(With input from Reuters)