On August 18, 2011, a series of cross-border attacks with parallel attacks and mutual cover was carried out in southern Israel on Highway 12 near the Egyptian border by a squad of presumably 12 militants in four groups. The attacks occurred after Israel's interior security service Shin Bet had warned of an attack by militants in the region and Israeli troops had been stationed in the area. The militants first opened fire at an Egged No. 392 bus as it was traveling on Highway 12 in the Negev near Eilat. Several minutes later, a bomb was detonated next to an Israeli army patrol along Israel's border with Egypt. In a third attack, an anti-tank missile hit a private vehicle, killing four civilians. Eight Israelis – six civilians, one Yamam special unit police sniper and one Golani Brigade soldier—were killed in the multiple-stage attack. The Israel Defense Forces reported eight attackers killed, and Egyptian security forces reported killing another two. Five Egyptian soldiers were also killed. According to Egypt, they were killed by Israeli security forces chasing militants across the Egyptian border, while an Israeli military officer initially said they were killed by a suicide bomber who had fled across the border into Egypt. The five deaths triggered a diplomatic row between Egypt and Israel and led to mass protests outside the Israeli embassy in Cairo. According to media reports, Egypt threatened to withdraw its ambassador to Israel, but Egypt's foreign minister later denied this. Israel expressed regret over the deaths, and sent a letter of apology to Egypt. The IDF was ordered to conduct a military probe of the incident, and on August 25, 2011, Israel agreed to a joint investigation with Egypt of the events. The identity of the attackers, three of whom were reportedly Egyptian, is not widely agreed upon, and so far no group took responsibility for the attacks. The Israeli government accused the Palestinian Popular Resistance Committees (PRC), a Gaza-based coalition of Palestinian militant groups, of orchestrating the attacks, but the PRC denied involvement. However, Israel attacked seven targets in the Gaza Strip immediately after the terror attacks in the Negev, killing five members of the PRC, including its leader. On August 21, 2011, an informal ceasefire was called by Israel and Hamas after days of escalating violence in which fifteen Palestinians were killed and many were wounded. More than 100 rockets and mortar shells were