Islamic State militants have launched a wave of attacks on the security forces in Egypt's restive Sinai Peninsula.
The military said 10 soldiers had been killed or wounded along with 39 "terrorists" in near-simultaneous raids on checkpoints near Sheikh Zuweid.
But security and medical sources said as many as 50 soldiers had died.
Clashes are continuing in the area, with militants reportedly roaming the streets of Sheikh Zuweid and besieging the town's main police station.
Islamic State's local affiliate, Sinai Province, said in a statement posted online that it had targeted 15 security sites and carried out three suicide attacks.
The assault is the biggest since jihadists based in Sinai stepped up their attacks after the military overthrew Islamist President Mohammed Morsi two years ago. At least 600 police and armed forces personnel have since been killed.
Wednesday's attacks came two days after the assassination of Egypt's public prosecutor, Hisham Barakat, in the capital Cairo.
In a speech at Mr Barakat's funeral on Tuesday, President Abdul Fattah al-Sisi promised legal reforms to ensure death sentences could be enforced more swiftly for those convicted of acts of terrorism.