The UK and the European Union have agreed a deal on Brexit – which will now be put to British members of parliament in a special session on Saturday.

"We've got a great new deal that takes back control," UK Prime Minister Boris Johnson tweeted, repeating a key Leave campaign message from the UK's 2016 referendum.

Later, standing alongside European Commission President Jean-Claude Juncker at the start of the EU leaders' summit in Brussels, he added: "I hope very much now that my fellow MPs in Westminster do now come together to get Brexit done to get this excellent deal over the line."

Juncker, who got EU leaders' backing at the summit, called it "a fair and balanced agreement" and a "testament to our commitment to find solutions." 

At the pre-summit press conference with Johnson, he appeared to rule out the chance of any further extension to Brexit.

"There will be no prolongation. There is not an argument for further delay – it has to be done now. We have a deal. The British prime minister has to make sure it passes the hurdles of the British parliament. I was ruling out any sort of prolongation. We have a deal," he said.

"I'm satisfied that we were able to find a deal. I'm sad that Britain will be leaving the European Union," he said.

However Johnson faces a battle to get the deal backed by MPs, with the main opposition, anti-Brexit MPs and Northern Ireland's Democratic Unionist Party (DUP) all saying they will vote against it. 

The announcement of the deal came after intense negotiations, with the key issue being what happens at the Northern Ireland border after the UK leaves the EU, which is due to happen on 31 October.

Johnson's predecessor as UK prime minister, Theresa May, failed three times to get MPs to back the deal she negotiated with the EU. Johnson, who backed Brexit in the original 2016 referendum, hopes he has tackled the issues that meant some pro-Brexit MPs opposed May's plan.

Read the full Withdrawal Agreement

Read the revised political declaration on the UK and EU's future relations

Johnson's hopes of winning a parliamentary vote were hit when the DUP said it could not support the version it had seen.

"As things stand, we could not support what is being suggested on customs and consent issues and there is a lack of clarity on VAT," DUP leader Arlene Foster and deputy leader Nigel Dodds said in a statement.

The support of the DUP, which backs Johnson's government, is crucial as some hardline Brexiteers in his party say they will be swayed by its stance on the most difficult part of any agreement – the Irish border riddle.

Johnson, who has no majority in the 650-seat parliament, may need the support of the DUP, which has 10 seats.

Northern Ireland, which has the UK's only land border with another EU state, has been a thorn in the side of negotiators trying to find a way to withdraw from the bloc without creating a so-called hard border.

Decades of violence in the region was largely ended by a 1997 agreement that enshrined the idea that citizens could pass from one side to the other without checks, something the government in Dublin has insisted cannot change.

Jeremy Corbyn, the leader of the UK's official opposition Labour Party, said he was "unhappy" with the deal and would vote against it. MPs in his party said they had been told to vote for another referendum on Saturday.

Simon Coveney, Ireland's foreign minister, welcomed the new Brexit deal struck on Thursday between London and Brussels, calling it a "big step forward" that "protects the core Irish interests."

Johnson became prime minister in July with a pledge to deliver Brexit with or without a deal on 31 October.

But MPs opposed to a no-deal exit from the EU passed a law which means that if a deal is not backed by MPs by this Saturday, Johnson has to write to the EU asking for a delay to Brexit until 31 January. 

It is widely expected that if this happens, there would be a general election in an effort to break the deadlock on the issue.