A roadside bomb targeting a military checkpoint in Egypt's north Sinai town of Sheikh Zuweid has killed at least 25 Egyptian soldiers and injured another 26, according to local reports.
The attack happened near the border with the Gaza Strip, and was likely caused by a suicide bomber, although further reports said rockets and mortar bombs were also used.
State media said that clashes are ongoing near the site where the soldiers were killed.
"Heavily armed militants, armed with grenades, rockets and automatic rifles [are attacking] reinforcements at the military checkpoint", reported the Egyptian Streets website.
Eyewitnesses had earlier heard a loud explosion near the north Sinai city of al-Arish. Ambulances are still waiting to enter the area as security forces scout for other explosives.
Egypt's President Abdel Fattah al-Sisi has called for an emergency meeting with the national security council to discuss the incident.
Earlier in September 2014, a blast struck a convoy in the Sinai peninsula killing at least 11 Egyptian border police officers.The soldiers were travelling through the village of Wefaq, near the Gaza border, when the bomb was detonated, allegedly by remote control. Two of them were killed instantly by the bomb and the others were shot dead as they tried to flee.
Islamist militants in the Sinai have targeted Egyptian policemen and soldiers since the then-army chief Abdel Fattah al-Sisi ousted democratically elected president Mohammed Morsi, of the Muslim Brotherhood, in the July 2013 coup d'etat.
Several jihadists belonging to the main Islamist group in the area, Ansar Beit al-Maqdis, have been shot dead in security operations.
Earlier, the group released a video showing the beheading of four men they accused of working for Israeli intelligence and said it carried out the execution in retaliation for a July 2014 airstrike that killed three of its fighters.
Ansar Beit al-Maqdis (Champions of Jerusalem) has been operating in the restive Sinai Peninsula since the Arab Spring uprising against former Egyptian President Hosni Mubarak in 2011.
The group is also known to have carried out attacks against Israel. Since former army chief Abdel Fattah al-Sisi took power in Egypt, the country's police and army have been targeted.
According to Egyptian media, the three Ansar Beit al-Maqdis fighters killed in July were hit by an Israeli UAV, as they were attempting to fire rockets across the border.
However, Egyptian authorities said they had carried out the strike and denied an Israeli drone had crossed into the country's airspace.
Inspired by al-Qaeda, Ansar Bayt al-Maqdis is not known to be affiliated with the Islamic State.