Yousef Bin Ahmad Al-Othaimeen, who heads the Saudi- headquartered organisation, said acts of terrorism contradict the fundamentals of Islam.
The OIC is comprised of 57 Muslim- majority countries from around the world.
Meanwhile the six-nation Gulf Cooperation Council, which includes Saudi Arabia, the United Arab Emirates, Qatar, Kuwait, Bahrain and Oman, described the attack as "a terrible crime that is incompatible with all values and principles of humanity."
The Saudi Press Agency reports that Saudi Arabia's King Salman sent a cable of condolences to British Prime Minister Theresa May in which he says the kingdom "strongly condemns this terrorist act."
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