At least 16 Egyptian policemen were killed in the attack which occurred two weeks ago.
A previously unheard of militant group with links to Al Qaeda claimed responsibility on Friday for an attack in Egypt's Western Desert that killed at least 16 policemen two weeks ago.
The group announced the start of a war against the Egyptian state.
The new group, Ansar al Islam, gave no evidence for its claim of responsibility for the October 21 attack but said Abu Hatem Emad al Din Abd al Hamid, a fighter suspected by the authorities of involvement, was one of its leaders.
He was killed this week in an air strike.
"We have started our jihad with the battle of the Lion's Den in the Bahariya Oasis area on the borders of Cairo and were victorious against the enemy's campaign," the statement said.
Two security sources and a forensic doctor said DNA analysis of bodies of militants killed in the air raid showed Hamid was among them.
Three security sources said at the time of the October 21 attack that at least 52 police officers and conscripts had been killed when their patrol was struck by militants.
The interior ministry denied that figure the next day, saying 16 policemen had been killed.
The attack was the latest to plague Egypt's security forces who face a Daesh insurgency, mostly focused in the Sinai Peninsula, but which has expanded to mainland Egypt.
Former-military officers-turned terrorists
Security sources said Hamid was the deputy of Hesham al Ashmawy, a former Egyptian military officer who operated out of the city of Derna, across the border in Libya, and is blamed for past attacks.
Ashmawy and Hamid graduated from Egypt's military academy the same year and were both fired from the army for adopting radical beliefs.
"We have information that Ashmawy and Abd al Hamid broke away from (Daesh) after a third colleague of theirs was killed and also for doctrinal issues," said one officer with Egypt's Homeland Security agency on condition of anonymity.
Security sources say Ashmawy has carried out some of the most high-profile attacks in Egypt, including the attempted assassination of a former interior minister in 2013 and the killing in 2015 of Egypt's top public prosecutor in a car bomb.
Ashmawy is known for being loyal to Al Qaeda, which means that if Ansar al Islam's claim of responsibility is verified it could herald the emergence of a new Egyptian cell of the network founded by Osama bin Laden.
Growing terrorism in Egypt
In recent years, most attacks on security forces in Egypt have been blamed on fighters claiming allegiance to Daesh.
President Abdel Fattah el Sisi appointed a new military chief of staff after the militants struck. The Interior Ministry dismissed several high-ranking officials.
Security forces responded with two raids in the span of a week, killing dozens of militants and freeing a police officer who was taken hostage during the attack.
Ansar al Islam said it used rocket-propelled grenades in the attack but provided no estimate for how many people were killed. It said the Egyptian air force struck 11 days later, killing several members including Abd al Hamid.
Ansar al Islam's statement was carried by groups with Al Qaeda links, including Guardians of Sharia, whose social media feeds carry statements from Al Qaeda chief Ayman al Zawahiri.