Smoke billowed in the sky as Egyptian helicopter gunships rocketed suspected Islamic militant hideouts in the lawless northern Sinai Peninsula for a second day on Sunday, killing 11 suspected fighters as part of the largest military offensive in the region in years, military officials said.

They say the assault aims to drive out al-Qaida inspired groups from several villages of the restive border region, where militants have established strongholds and stockpiled an unprecedented amount of weapons.

Also Sunday, a militant group in northern Sinai allegedly claimed responsibility for a failed assassination attempt on the country’s interior minister last week. In a statement attributed to Ansar Jerusalem posted on militant websites, the Islamic extremist group claimed it was behind the attack on Mohammed Ibrahim. The statement says military chief Gen. Abdel-Fattah el-Sissi, who led a coup against former Islamist President Mohammed Morsi, is another target.

A military official said 11 militants and one soldier were killed in the fighting on Sunday. He said 10 militants had been arrested. A day earlier two soldiers and nine militants were killed in the offensive. The official spoke anonymously because he was not authorized to release the information.

Gen. Osama Askar of the 3rd Army told reporters troops had seized at least 10 shoulder-fired Sam-7 anti-aircraft missiles a day earlier. They were found in a mosque and in homes of suspected militants in the town of Sheikh Zuweyid, near the border with the Gaza Strip and Israel.

Western officials say thousands of shoulder-launched missiles went missing from Libyan arsenals since that country’s 2011 civil war. Egyptian authorities say Libyan missiles have been smuggled into the Sinai, and some of those have gone on through underground tunnels to Gaza.

Sunday’s airstrikes targeted the villages of el-Mahdiya and el-Moqataa on the outskirts of Rafah and Sheikh Zuweyid. One official said U.S.-made Apache helicopters hit shacks, houses, olive farms and cars used by militants.

The strikes paved the way for a ground offensive, allowing troops backed by armored vehicles to sweep homes of suspected militants.

Armed Forces spokesman Col. Ahmed Mohammed Ali said that helicopters had provided air cover for what was “the biggest security operation” in the northern Sinai in years. Ali’s statement, posted on his official Facebook page, also said that 118 houses and farms used as hideouts had been demolished in the operation by Saturday.

A second military official in Cairo said the military found heavy weapons, explosive belts for suicide bombers, mortars, RPGs, anti-aircraft missiles and maps with positions of the military in the region.

In Cairo, a virtually Islamist-free panel tasked to amend the country’s now-suspended 2012 constitution convened for the first time as authorities push to roll back Morsi’s legacy and implement a transition plan for fresh elections.

Islamists have seen their clout drastically reduced — a radical reversal from the initial post-Mubarak period when they formed new political parties and won elections.

In its first session, the 50-member panel dominated by secularists and liberals chose as its head veteran diplomat and former Arab League chief Amr Moussa. The panel has two months to finalize constitutional amendments already proposed by 10 experts before the public votes on the text.

It will be the third time since Egypt’s 2011 uprising that the constitution has been amended.