"He will receive close monitoring during the early phase of his recovery," a statement about the prime minister's condition said.
Johnson's comments to Iran's president came after Trump urged European allies, as well as Russia and China, to withdraw from the 2015 treaty.
"I think he was asking a question, to be fair, that a lot of British reporters would have asked," the embattled British leader said.
Theresa May, the British prime minister, danced out onto the stage at her speech to the annual Conservative Party conference.
May says she wants to help those who are just managing to get by.
May was appointed PM after David Cameron visited the Queen to formally resign.
Child abuse to be on par with organised crime after Rotheram scandal where 1,4000 children were abused.