BENGHAZI, Libya – Heavily armed militants used a protest of an anti-Islam film as a cover in their deadly attack on the U.S. Consulate, screaming “God is great!” as they scaled its outer walls and descended on the main building, a witness and a senior Libyan security official said Thursday.

The account, the most detailed yet of the rampage that killed the U.S. ambassador and three other Americans, came as the Libyan government said four people suspected in the attacks had been arrested and more were being sought.

The security official, eastern Libya’s deputy interior minister, Wanis el-Sharef, said it was a two-pronged attack. He said that hours after the crowd stormed the consulate Tuesday night, the militants raided a safe house in the compound just as U.S. and Libyan security arrived to evacuate the staff, suggesting infiltrators within the security forces may have tipped off the militants to the location of the safe house.