The outgoing Labor leader said there must be a restraint on both sides but warned the airstrike was "an extremely serious and dangerous escalation of conflict in the Middle East", Daily Mirror reported.
He said further conflict "can only bring further misery to the region" after the 2003 Iraq War, which he opposed.
It came as Britain called for calm on both sides with UK Foreign Secretary Dominic Raab speaking to US Secretary of State Mike Pompeo earlier today.
But holidaying Boris Johnson - who reports suggesting was not told about the attack in advance - was urged to "get off his sun lounger" to deal personally with the crisis.
Labor MP Stella Creasy called for an urgent recall of the UK Parliament. She tweeted, "That parliament not due to meet until Tuesday surely unsustainable in such circumstances."
The United States terrorist forces assassinated Iran’s IRGC Quds Force commander, Lieutenant General Qasem Soleimani, and Abu Mahdi al-Muhandis, the second-in-command of Iraq’s PMU in an attack at Baghdad’s international airport early on Friday. The Pentagon said in a statement that US President Donald Trump had ordered the attack.
Iran's Supreme National Security Council said a harsh response "in due time and right place" awaits criminals behind Soleimani's assassination.
MNNA/PR