Rishi Sunak’s Brexit deal needs “re-working and change” before the DUP can support it, the party’s leader Jeffrey Donaldson has declared.

In a major blow for the prime minister, Donaldson said the Windsor Framework did not go far enough to address unionists’ concerns.

The agreement, which Sunak struck with European Commission president Ursula von der Leyen earlier this month, aims to solve the problems caused by the Northern Ireland Protocol signed by Boris Johnson three years ago.

He said it would remove the current customs border in Irish Sea while also giving the UK government an effective veto on new EU laws being imposed on Northern Ireland.

MPs are to be given a Commons vote on the deal, with the DUP’s support being seen as crucial to prevent a major rebellion by Brexiteer Tories.

The DUP’s support for the Framework is also seen as essential for the party to agree to enter a power-sharing government at Stormont with Sinn Fein.

But speaking during a visit to Washington, Donaldson said as it currently stands, his party cannot back it.

In a statement, he said: “It is my current assessment that there remains key areas of concern which require further clarification, reworking and change, as well as seeing further legal text.”

He added: “What is in this Windsor Framework is insufficient. It does not meet all of our requirements, it does not go as far as we need, in terms of our tests and in terms of restoring fully Northern Ireland’s place within the internal market of the United Kingdom.

“So, we need to see the legislative safeguards, we need to see the legislation that is going to ensure the Government honours the commitments it has made.”