London, Aug 3 : The UK's Foreign, Commonwealth & Development Office (FCDO) has summoned Iran's ambassador after a drone attack allegedly carried out by Tehran on an Israeli-owned oil tanker in the northern Indian Ocean. On Monday, James Cleverly, the UK's Minister for the Middle East, summoned Mohsen Baharvand, the Iranian Ambassador to Britain "in response to the unlawful attack on a merchant vessel off the coast of Oman on 29 July, in which a British national and Romanian national were killed", Xinhua news agency quoted the FCDO as saying a statement. "Minister Cleverly reiterated that Iran must immediately cease actions that risk international peace and security, and reinforced that vessels must be allowed to navigate freely in accordance with international law," the statement said. The UK, the US, and Israel have accused Iran of carrying out the attack, which Tehran has denied. Israeli Prime Minister Naftali Bennett said that his country had "intelligence evidence of Tehan's involvement in the incident". In response to Monday's development, Iran has also summoned the British charge d'affaires in Tehran. In a statement, the Iranian Foreign Ministry said: "The source of instability in the Persian Gulf is not Iran; it is rather the presence of warships and military forces of countries from outside the region." Iran also warned against "any adventurism by the occupying regime of Israel or others in the region". "Iran's definite policy is defending itself and giving a crushing, timely and proportionate response to any act of adventurism," the statement added. Zodiac Maritime, a London-based firm owned by Israeli billionaire Eyal Ofer, said that its oil tanker "Mercer Street" was attacked on July 29 in the northern Indian Ocean, and two crew members onboard, a Romanian and a Briton, were killed. So far, no one has claimed responsibility for the attack. Iran and armed groups associated with it have been blamed for using drone attacks to target its ships in the Gulf in previous cases. The incident marked the first time that such an attack resulted in fatalities. /IANS