Militants fired rocket-propelled grenades at two buses in the Sinai on Monday killing 24 policemen, as Egypt's military chief vowed a "forceful" response to violence roiling the Arab world's most populous nation.
The attack was the deadliest of its kind in years and raises fears of a return to the wave of deadly violence linked to Islamist groups that swept Egypt in the 1990s.
It comes as the country's army-installed authorities wrestle with a deep political crisis and bloodshed that has left almost 800 people dead in days of clashes between Islamist protesters and security forces in Cairo, Alexandria and other flashpoints.
Among those killed in the latest violence were 36 Islamist detainees who died in police custody overnight, with authorities saying they had suffocated on tear gas fired after they took a police officer hostage.
The Sinai attack left at least two other policemen injured, with unknown militants firing on buses carrying police as they headed towards the town of Rafah on the border with the Palestinian Gaza Strip.
The security situation in the Sinai Peninsula, which borders both Gaza and Israel, has deteriorated since 2011, when president Hosni Mubarak was overthrown.
But it has become significantly worse since the army ousted president Mohammed Morsi on July 3, with near daily attacks by militants targeting police and military installations.
The violence highlights the government's loose grip on the peninsula that is home to lucrative tourist resorts.
Elsewhere in the country, bloodshed sparked by the August 14 security force crackdown on pro-Morsi protest camps showed little sign of abating.
Authorities said 36 Islamist detainees died after police fired tear gas in a bid to free a police officer taken hostage by prisoners.
But the Muslim Brotherhood, the once-banned movement from which Morsi hailed, held the police accountable.
"The murder of 35 detained anti-coup protestors affirms the intentional violence aimed at opponents of the coup, and the cold-blooded killing of which they are targets," it said in a statement in English.
The deaths of the detainees came hours after military chief Abdel Fattah al-Sisi warned that security forces would confront any violence from protesters.
"We will never be silent in the face of the destruction of the country," said Sisi, who overthrew Morsi on July 3 after protests against the Islamist president's rule.
"We are very prepared for this," he said, pledging a "forceful" response to further attacks on police stations and government buildings.
