At least 25 extremists were killed in a military raid that lasted until early Saturday morning in Egypt's North Sinai province, said a security source.
"It is the most violent military operation in the history of Egypt's war against terrorism," the source told Xinhua on condition of anonymity, noting that the raid, in the city of Sheikh Zuweid near the Israeli border, started on Friday afternoon.
According to the source, the extremists belonged to the Sinai-based al-Qaida-inspired Ansar Bayt al-Maqdis group, which has claimed responsibility for a number of deadly terrorist attacks since the ouster of former President Mohamed Morsi last year.
"The massive military ground and air raid targeted the group's hideouts in Sheikh Zuweid's towns and it was supported by military Apaches," said the source.
The raid came in response to the killing of two police and military officers by gunmen on Friday afternoon.
Last week, militants killed 22 military officers at a checkpoint in Al-Wadi al-Gadid province, about 600 km southwest of the capital Cairo.
Extremist self-proclaimed Islamist groups which refer to Morsi's overthrow as "a military coup" say their attacks were in retaliation for the harsh security crackdown on the major sit-ins of Morsi's supporters in August 2013, which left at least 1,000 killed and thousands more arrested.