Donald Trump to announce Iran nuclear decision on Tuesday as Boris Johnson warns him not to 'throw the baby out with the water'

Donald Trump announced he will reveal his decision on whether to abandon the Iran nuclear deal on Tuesday, just as Boris Johnson, the Foreign Secretary, warned him that backing out could spark an "arms race in the Middle East".

Mr Trump has frequently promised to reimpose sanctions on Tehran, effectively killing off the 2015 agreement, unless more is done to rein in Iran's missile programme and thwart its ambitions in the Middle East.

However, aides on Monday night said nothing was certain until Mr Trump made his announcement.

The brinksmanship has sparked an intense round of 11th-hour diplomacy.

On Monday, it was Mr Johnson's turn as he appeared on Fox News, the President's favourite TV channel, to issue his message.

"We think what you can do is be tougher on Iran, address the concerns of the president and not throw the baby out with the water," he said.

He argued that despite the deal's weaknesses, backing out of it could lead to Iran developing nuclear weapons - a move which could prompt Saudi Arabia and the Emirates to follow suit. 

"We don't want to go down that route," he said.

With anticipation mounting, Mr Trump moved up his decision from a Saturday deadline. He said on Twitter that he will be announcing his decision on the Iran Deal on Tuesday from the White House at 2pm local time. 

Mr Johnson is on a two-day trip to Washington to meet with Mike Pence, the Vice President, National Security Adviser John Bolton and foreign policy leaders in Congress to persuade them not not to back out of the deal. 

Under the international agreement, Iran has limited its nuclear activities in return for eased economic sanctions.

Appearing on Fox & Friends, which Mr Trump watches regularly, Mr Johnson began by saying the US president was "right to see flaws" in the current deal, saying "he's set a very reasonable challenge to the world".

"Iran is behaving badly...we've got to stop that," he said. 

But the Foreign Secretary warned that without the accord, Iran could develop a nuclear weapon and "an arms race in the Middle East".

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"You're going to have the Saudis wanting one, the Egyptians, the Emiratis, it's already a very, very dangerous state at the moment, we don't want to go down that route."

Mr Johnson said a key flaw was the so-called "sunset clause" in the deal, which currently allows Iran to swiftly develop enrichment programmes after 2025 without economic sanctions.

"We've got to fix the flaws in the deal", he said. 

But argued that solution was to "fix the flaws in the deal", saying "there doesn't seem to me at the moment to be a viable military solution".

What is the Iran nuclear deal?

Britain, France and Germany have been lobbying Mr Trump's team for weeks in an effort to preserve the agreement, which was signed during the Obama administration, and includes Russia and China as signatories.

Emmanuel Macron, the French president, used his State Visit at the White House to urge Mr Trump to consider the consequences of withdrawing. 

European leaders are trying to convince Mr Trump to keep the deal but add new arrangements for tackling Iran's missile programme and regional ambitions.

Mr Johnson questioned what steps the West would take to block Iran's nuclear activity, saying "Plan B does not seem to me to be particularly well developed at this stage".

"Are we seriously saying that we are going to bomb those [enrichment] facilities at Fordo and Natanz?" he asked.

Before Fox Mr Johnson also appeared on US network MSNBC, on which Mr Trump regularly appeared during his election campaign.

"We're talking now about the way the United States acts in the world and you see some very strong and original decisions by the president," he said. "This stuff he's doing in North Korea - fascinating the way he's playing that, taking a very tough line on Iran."

The Foreign Secretary added that he was looking forward to Mr Trump's visit to the UK on July 13.