Egyptian military helicopters hit militants in Sinai on Sunday as an Al-Qaeda inspired group in the peninsula claimed credit for a bombing that targeted the interior minister last week.
The Ansar Beit al-Maqdis group said in a statement one of its suicide bombers was behind Thursday's blast in Cairo targeting the convoy of interior minister Mohamed Ibrahim, who survived the attack.
Its statement, posted on jihadist forums, came as military helicopters launched air strikes for a second day on suspected militant hideouts in north Sinai, witnesses said.
The military has poured troops and armour into Sinai to quell an insurgency that surged after the army overthrew Islamist president Mohamed Morsi on July 3.
The army described the operation as "the largest military operation to purge Sinai of terrorism."
The military has so far killed "nine terrorists" and destroyed militant hideouts and weapons depots, said army spokesman Colonel Ahmed Aly in a statement on Facebook.
It was not immediately possible to authenticate the statement by Ansar Beit al-Maqdis -- Partisans of Jerusalem in English -- which was accompanied by what appeared to be still images of the bombing that targeted Ibrahim.
"God has allowed your brothers in Ansar Beit al-Maqdis to shatter the security organisation of the murderer Mohammed Ibrahim through a martyrdom operation," the group said in the statement, pledging further attacks.
The group blamed Ibrahim and army chief Abdel Fattah al-Sisi for the killings of hundreds of Islamist supporters of president Mohamed Morsi, overthrown by the military in a popularly backed coup on July 3.
"We call on all Muslims in Egypt to stay away from all military and interior ministry installations to preserve their lives," it added.
If proven, the group's claim would show it has the reach to strike in Egypt's capital and elsewhere in the country even as the military engages it and other jihadist groups in Sinai.
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Militants in Sinai had limited their attacks to the peninsula and neighbouring Israel, bombing tourist resorts in south Sinai between 2004 and 2006, and had never before claimed credit for attacks elsewhere in Egypt.
Militants have launched almost daily attacks on the security forces since the military overthrew Morsi.
Deadly violence had surged in the peninsula after former president Hosni Mubarak was toppled in a popular uprising in 2011, creating a security vacuum.
For years Sinai has defied the central government's authority, with its Bedouin population complaining of poverty and discrimination.
The surge in militant attacks there and elsewhere around the country has raised fears of a revival of the Islamist insurgency that plagued Egypt in the 1990s.
On Tuesday, the military staged intense strikes in the Sinai which a security source described as the "biggest aerial assault of its kind" in the peninsula.
On August 19, militants killed 25 policemen in the Sinai, the deadliest attack on security forces in the country in years.
The army has killed around 100 Islamists in the area over the past two months, and the militants killed 58 policemen, 21 soldiers and 17 civilians there, according to an AFP tally.
The army, meanwhile, continued demolishing smuggling tunnels to Gaza, with a security official saying on Sunday more than 90 percent of the tunnels have now been destroyed.
The tunnels have been a lifeline for the flow of food, clothing, building materials and fuel into the impoverished territory, which Israel has blockaded since 2006.
In February, Hamas said it had closed hundreds of tunnels used for smuggling in Rafah.