At least 235 people have died after militants attacked a crowded mosque in North Sinai, detonating a bomb and gunning down worshippers in the deadliest such attack in Egypt's modern history.
No group has yet claimed responsibility for Friday's attack, but since 2013 Egyptian security forces have battled an Islamic State affiliate in the mainly desert region, and militants have killed hundreds of police and soldiers.
State media are showing images of bloodied victims and bodies covered in blankets inside the Al Rawdah mosque in Bir al-Abed, west of El Arish, the main city in North Sinai.
Worshippers were finishing noon prayers when a bomb exploded and witnesses say around 40 gunmen were waiting outside and opened fire as the worshippers fled.
"Four groups of armed men attacked the worshippers inside the mosque after Friday noon prayers. Two groups were firing at ambulances to deter them, said Mohamed, a witness.
The public prosecutors' office said in a statement 235 people had been killed and 109 more wounded.
Hours after the attack, Egypt's military launched air strikes on targets in mountainous areas around Bir al-Abed, security sources and witnesses said.
"The armed forces and the police will avenge our martyrs and restore security and stability with the utmost force," Egypt's President Abdel Fattah al-Sisi said in a televised address.
"What is happening is an attempt to stop us from our efforts in the fight against terrorism, to destroy our efforts to stop the terrible criminal plan that aims to destroy what is left of our region."
Egypt later said it would delay the opening of the Rafah border crossing to Gaza after the attack due to security concerns. The crossing had been due to open for three days beginning on Saturday.
Striking at a mosque would be a change in tactics for the Sinai militants, who have usually attacked troops and police and Christian churches.
US President Donald Trump described the assault as a "horrible and cowardly terrorist attack" in a Twitter post.
"The world cannot tolerate terrorism, we must defeat them militarily and discredit the extremist ideology that forms the basis of their existence," he added.
Trump later called Sisi to express his condolences.
North Sinai, which stretches from the Suez Canal eastwards to the Gaza Strip and Israel, has long been a security headache for Egyptian security forces because of smuggling.
Sisi has support from some Bedouin tribal leaders, who have helped the army locate weapon-smuggling routes used by jihadi groups, security officials said.
Local militant group Ansar Bayt al-Maqdis, once allied to al-Qaeda, split from it and declared allegiance to Islamic State in 2013.
Bloodshed in the Sinai worsened after 2013 when Sisi led the overthrow of President Mohamed Mursi of the Muslim Brotherhood.
Islamic State earlier this year posted a video of the beheading of two Sufis in northern Sinai, accusing them of practicing "sorcery".
In July this year, at least 23 soldiers were killed when suicide car bombs hit two military checkpoints in the Sinai, in an attack claimed by Islamic State.
Militants have tried to expand their operations into Egypt's heavily populated mainland, hitting Coptic Christian churches and pilgrims. In May, gunmen attacked a Coptic group travelling to a monastery in southern Egypt, killing 29.