ISMAILIA, Egypt (Reuters) - Militants attacked a security convoy in Egypt s strife-torn Sinai Peninsula, killing at least 18 policemen in a blast and a gun battle on Monday, sources said - an assault claimed by Islamic State. The attackers detonated an improvised explosive device and managed to destroy three armored vehicles and a signal-jamming vehicle near Arish, the capital of North Sinai province, the security and medical sources said. The attack turned into a gunfight and the militants also opened fire on ambulance workers, injuring four, the sources told Reuters.  At least 18 policemen, two of them officers, died in the violence, and a brigadier general lost a leg in the blast, several sources at Arish hospital said. Islamic State claimed responsibility for the attack in a statement posted by its news agency Amaq. The Sunni Muslim militants are waging an insurgency in the rugged, thinly populated Sinai, aiming to topple the government of President Abdel Fattah al-Sisi.  Militants have killed hundreds of soldiers and police there since 2013, when the military, led by Sisi, ousted Egypt s Islamist president Mohamed Mursi after mass protests against his rule. At least 23 Egyptian soldiers were killed when suicide car bombs tore through two military checkpoints in North Sinai in July, in one of the bloodiest assaults on security forces in years. The Interior Ministry said several policemen were killed or injured in the attack, without giving figures. The prime minister s office called it a  traitorous incident .  Prime Minister Sherif Ismail affirmed the state s determination to fight these criminal actions that target the safety and will of citizens with its full force,  a government statement said. The United States strongly condemned the attack and said it would  continue to stand with Egypt as it confronts the threat from terrorism,  the State Department said. 