Egypt's military and police forces have killed 53 Islamist militants and arrested 680 suspects in a week-long offensive to crush insurgents that is focused on the Sinai Peninsula, a military spokesman said on Thursday. President Abdel Fattah al-Sisi, who is seeking re-election in March, ordered the armed forces in November to defeat militants within three months after an attack on a mosque in Sinai killed more than 300 people. The attack was the deadliest of its kind in Egypt, which is the Arab world's most populous country and a main regional ally of the United States. The security operation, which involves the army, navy, air force and police, began last Friday and targeted "terrorist and criminal elements and organisations" in north and central Sinai, parts of the Nile delta and the western desert, Colonel Tamer al-Rifai told a news conference broadcast on state television on Thursday. Rifai said forces have destroyed over 1,000 kg (2,205 lbs) of explosives, 378 militant hideouts and weapon storage facilities including a media centre used by the militants. He added that 680 people, some of them suspected militants or wanted criminals, were also detained in the operation. The air force, which has carried out more than 100 airstrikes in northern and central Sinai since the operation began, has focused on militant hideouts outside residential areas to avoid hitting civilians, air force Brigadier General Alaa Dawara said. Major General Yasser Abdel Aziz of the Military Operations Authority said the operation would end when Sinai was free of "terrorists". "It could be extended or shortened according to the situation and that is what will be determined in the coming days," Abdel Aziz told journalists. He said after the military operation, Egyptian authorities would push ahead with a comprehensive development plan for Sinai. Outside the peninsula, the Egyptian military said the operation also covers parts of the Nile Delta and the Western Desert, where other militants have waged attacks, some believed to be staged out of neighbouring Libya. Islamist insurgents have been targeting security forces since 2013 when the army led by Sisi, then the army chief, ousted President Mohamed Mursi, of the Muslim Brotherhood, following mass protests against his rule. Islamic State, in its weekly newspaper al-Naba, called for attacks inside Egypt to show the campaign was a failure. "Any attack inside Egypt is bound to show . Sisi's allies that he is unable to control security in areas under his control," a commentary article said. Security forces foiled a planned attack on a police ambush in Minya province, some 250 km (150 miles) south of Cairo and arrested one assailant, state news agency MENA reported late on Thursday citing a security source, but gave no further details. Some local residents have raised concerns over food and medicine shortages in the peninsula after the army blocked all access to the area. Rifai said the armed forces has cooperated closely with local authorities to coordinate the delivery of food, medical assistance and other supplies in compliance with local and international laws and human rights norms.