The Egyptian president has vowed to "respond with brutal force"
The number of people known to have died in a gun and bomb attack on a mosque in Egypt has risen to more than 300.
The death toll is now at 305, including 27 children, the Egyptian state-owned MENA news agency has said.
A total of 128 people were also wounded in the attack at a mosque in the country's North Sinai province on Friday.
A bomb exploded in the al Rawdah mosque in Bir al Abed - before dozens of militants sprayed bullets into the crowds of people who ran outside to escape.
The country's chief prosecutor Nabil Sadeq has claimed the terrorists were carrying IS flags.
Egyptian armed forces say they've launched airstrikes against militants they believe were responsible for the attack.
Egyptian President Abdel-Fattah el-Sissi said the attack "will not go unpunished" and vowed to "respond with brutal force."
"The army and police will avenge our martyrs and return security and stability with force in the coming short period," he said in a televised speech.
The military said it carried out the air strikes in Sinai which hit several vehicles used in the attack and locations where weapons and ammunition were stocked, an army spokesman said.
Revealing more about the mosque attack, Mr Sadeq said there were between 25 and 30 gunmen who arrived at the mosque in five all-terrain vehicles.
The militants positioned themselves at the mosque's main door and 12 windows before opening fire on worshippers inside, he added.
They also set fire to seven cars belonging to worshippers to block roads.
The terror group has not claimed responsibility for the attack which is the deadliest in Egypt's modern history.
Middle East analyst Dr Hisham Hillyer says it's an ominous development:
“I think it is very concerning the precedent that it might lay down,” he said. “Because it means that they have redefined, yet again, what it means to be a civilian and who is considered to be a legitimate target.”
Abdullah Abdel-Nasser, 14, said he was attending prayers with his father when he heard a militant shouting for children to leave the mosque.
The boy, who was shot in the shoulder as he escaped, said: "I saw many people on the floor, many dead. I don't think anyone survived."
Mohammed Ali said 18 members of his extended family were killed.
He added: "Where was the army? (They are) only a few kilometres away. This is the question we cannot find an answer to."
No group has yet claimed responsibility for the attack but Egyptian state news agency MENA said they "appeared" to have been carried out by ISIS.
The mosque was attended by Sufi Muslims, who are seen as non-believers by ISIS.
Bir al Abed is in the volatile northern Sinai Peninsula, around 25 miles from the provincial capital of el Arish, which has been regularly targeted by ISIS militants in recent years.
US President Donald Trump described the attack as "horrible and cowardly."
The US President tweeted: "The world cannot tolerate terrorism, we must defeat them militarily and discredit the extremist ideology that forms the basis of their existence!"
Horrible and cowardly terrorist attack on innocent and defenseless worshipers in Egypt. The world cannot tolerate terrorism, we must defeat them militarily and discredit the extremist ideology that forms the basis of their existence!— Donald J. Trump (@realDonaldTrump) November 24, 2017
Cairo's international airport has boosted security following the attack, with troops seen patrolling passenger halls, conducting searches and manning checkpoints.
Egypt's government has declared three days of mourning, while the Eiffel Tower's lights were switched off at midnight on Friday in a show of solidarity.