The Prime Minister has said General Qassem Soleimani, the Iranian commander killed in a US air strike last week in Iraq, had the "blood of British troops on his hands".
Boris Johnson was addressing the House of Commons when he condemned Iran's attacks on military bases in Iraq.
The two bases targeted, at Al Asad and in Erbil, contained British and American personnel, with the Ministry of Defence confirming there were no UK or US casualties.
The UK has around 400 British Army soldiers deployed in Iraq.
At Prime Minister's Questions he echoed the comments made by Foreign Secretary Dominic Raab, telling MPs: "We of course condemn the attack on Iraqi military bases hosting coalition forces.
"Iran should not repeat these reckless and dangerous attacks but must instead pursue urgent de-escalation."
Boris Johnson said he opposed any further escalation of violence and told MPs: "As far as we can tell there were no casualties last night sustained by the US and no British personnel were injured in the attacks.
"We are doing everything we can to protect UK interests in the region, with HMS Defender and HMS Montrose operating in an enhanced state of readiness to protect shipping in the Gulf."
Answering a question from Labour leader Jeremy Corbyn about the legality of the drone strike that killed the Iranian general, the PM said the US had the right to defend its bases.
"Clearly the strict issue of legality is not for the UK to determine since it was not our operation," said the PM.
"But I think most reasonable people would accept that the United States has the right to protect its bases and its personnel."
The PM said Gen Soleimani had supplied "improvised explosive devices to terrorists, which I'm afraid killed and maimed British troops".
He added: "That man had the blood of British troops on his hands."