The Islamic State group claimed responsibility for attacking a remote Egyptian army outpost in the Sinai Peninsula with a suicide car bomb and heavy machine gun fire. The assault killed at least 23 soldiers in the deadliest attack in the turbulent region in two years, The Associated Press reports.

The IS made the claim after nightfall Friday, July 7, saying in an online statement that it had carried out the attack as the Egyptian army was preparing an assault on IS positions in Sinai.

Friday’s assault began in the early morning, when a suicide bomber rammed his vehicle into a checkpoint at a military compound in the village of el-Barth, southwest of the border town of Rafah.

Dozens of masked militants then descended on the site in 24 Land Cruiser SUVs and opened fire on the soldiers with machine guns, according to security officials.

The shooting lasted nearly half an hour, the officials added, speaking on condition of anonymity because of regulations. The troops at the compound were estimated to have numbered about 60.

When the attack subsided, the militants apparently looted the checkpoint, snatching weapons and ammunition before fleeing, the officials said. A number of militants were killed in the shootout, indicating the soldiers had fought back, and some of their vehicles were abandoned at the scene.

The suicide blast at the start of the attack likely disabled the checkpoint’s military communications system, prompting one of the officers to use his own cellphone to record an audio message and send it to a colleague via WhatsApp, seeking help and asking for prayers. The message was later widely circulated on social media.

“This might be the last seconds in my life,” a man’s voice calmly says in the recording. “Quickly, oh men, anyone who knows how to reach the command center, notify them to use artillery as we are still alive.”

He then praises God and ends by saying “we will either avenge them or die,” referring to his fallen colleagues.

The security officials initially put the death toll at 10 but later told The Associated Press that more bodies were pulled from under the rubble of a nearby building that was used as a rest house for troops.

According to the IS statement, a second car bomber was used in the attack to strike an army convoy sent as a reinforcement to the embattled soldiers. The authenticity of the IS claim could not be verified but it was circulated by IS supporters online and by the U.S.-based SITE Intelligence Group, which monitors jihadi websites.