US President Donald Trump has already criticised the prime minister for refusing to allow the use of UK bases in the initial strikes, and said he is “not Winston Churchill”.
The UK agreed on Sunday to a US request to use British military bases but only for defensive strikes on Iranian missile sites.
Trump said the initial decision was “shocking” and that the UK-US relationship was “not what it was”.
But Sir Keir insisted the special relationship between the US and the UK had not been fractured.
“Look, the special relationship is in operation right now,” he told reporters on Thursday.
“We’re sharing intelligence on a 24/7 basis in the usual way. That is the special relationship.”
Sir Keir, who chaired a meeting of the government’s emergency committee Cobra on Thursday, acknowledged that people are “worried sick about their family and friends who are caught up in this”.
“We will do everything we can to protect British lives,” he said.
The PM denied the UK was not prepared for the conflict, pointing out that Britain began pre-deploying assets to the region earlier this year – particularly Qatar and Cyprus – alongside the US and other allies.
Defence sources said 400 additional UK personnel had been sent over the past weeks to support air defence activities across the UK’s bases in Cyprus.
It comes after the government faced criticism for its response when British bases in Bahrain and Cyprus were struck at the weekend.
“A lot of pre-planning has gone into this and a lot of pre-deployment,” the prime minister said.
“I am satisfied we can keep our people safe.”
Along with the Typhoon jets which defence sources say will be “rapidly” deployed, two wildcat helicopters with anti-drone-capabilities will also arrive in Cyprus on Friday.
The British warship HMS Dragon will also sail to Cyprus, but Defence Secretary John Healey told the BBC it will arrive “within the next couple of weeks”.
It comes after a drone struck the runway at RAF Akrotiri on Sunday, causing what the Ministry of Defence described as “minimal damage”.