In the hours before President Donald Trump was to sit down for dinner with Chinese President Xi Jinping, his top military advisors called him to a secure room within his Mar-a-Lago estate where he ordered the Syrian missile strike.

After Tuesday’s deadly chemical weapons attack in northern Syria which killed 70 people including 20 children, the President immediately requested a list of options to punish Syrian President Bashar al-Assad.

By Thursday, his team had come up with three options, but Mr Trump was already back at his $175 million Florida estate for his first summit with the Chinese President when the top-secret briefing took place.

It has been revealed the briefing was conducted in a makeshift Situation Room by, among others, National Security Adviser Herbert “HR” McMaster and Secretary of Defense Jim Mattis, an official familiar with events told Reuters.

In a room not nearly as secure as the bunker in the White House, the advisors presented Trump with three options, quickly narrowed to two: bomb multiple airfields or a single, masive strike onthe Shayrat airfield near the city of Homs, where the military jet carrying the poison gas had taken off.

WH photo (ed for security): @potus receives briefing on #syria military strike fr Nat Security team, inc @vp , SECDEF, CJCS via secure VTC pic.twitter.com/aaCnR7xomR

— Kayleigh McEnany 45 Archived (@PressSec45) April 7, 2017

Elsewhere on the estate security was tight, with paid-up club members and guests looking forward to dinner, including Boston Celtics legend and NBA Hall of Famer John “Hondo” Havlicek, who was blowing out 77 candles on his birthday cake.

Meanwhile, after listening to an argument that it was best to minimise both Russian and Syrian casualties, Mr Trump chose the minimum option and ordered the hit on the Shayrat airfield, the official said.

Mr Mattis and Mr McMaster argued that choosing that target would draw the clearest line linking Assad’s use of nerve gas to the retaliatory strike, the official said.

Another official privy to the discussions said the Trump administration had formulated contingency plans for possible additional strikes to be launched as early as Friday night, depending on Assad’s response to the first attack.

Trump Created Makeshift Situation Room at Mar-a-Lago for Briefing on Syria Bombing. WITH 'QUIET AREA" SIGN ON DOOR https://t.co/uqhUliPXoK

— Jason Leopold (@JasonLeopold) April 8, 2017

Confronting his first foreign policy crisis, Mr Trump relied largely on seasoned military officers — Mr Mattis, a former Marine general, and Mr McMaster, a US Army lieutenant general — rather than the political operatives who dominated his policy decisions during the first weeks of his presidency, said three officials involved in the deliberations.

At a White House briefing on Friday, Secretary of Staye Rex Tillerson said Mr Trump made his dinner appointment and did “directly inform President Xi near the end of the dinner [on Thursday]” as the missiles that were launched “were impacting”.

“The President told President Xi that we had launched a strike against Syria as a result of Assad’s violation — multiple violations of the use of chemical weapons against his own citizens, including the killing of women, children, and babies.

“The President provided President Xi the number of missiles that were launched and explained the rationale behind it,” he said.