Palestinian travelers pass an Egyptian soldier standing guard on the Egyptian side of the Rafah border to cross over to Gaza at Rafah city, some 350 km northeast of Cairo, Friday. Egypt opened the Rafah border Friday to allow the return of Umrah pilgrims from Saudi Arabia and those stranded on their way back to Gaza, the state news agency said, citing a high-ranking official. — ReutersAL-ARISH — Egyptian troops and security forces Friday detained nine militants in northern Sinai believed to be behind a surprise attack last weekend that killed 16 Egyptian soldiers, a security official said. It was the first reported arrest in connection with the attack, which took place last Sunday and which sparked a major Egyptian military operation in the Sinai Peninsula aimed at stamping out militant groups that have become bolder and grown in numbers since the ouster last year of Hosni Mubarak. So far the effectiveness of the four-day-old operation is not clear. Despite the influx of troops, militants have continued low-level attacks on Egyptian troops and security forces. One famous checkpoint on the road linking Rafah border town with the city of Al-Arish comes under attack almost daily. Officials say that militants open fire at night, engage in brief firefight then flee. In the raid early Friday morning, troops stormed a house in Sheik Zweid, close to the Rafah border crossing with the Gaza Strip, and caught the nine suspected militants while they were asleep. Among them was Selmi Zeyoud, whom the official described as a “dangerous element" and a brother to a slain hardcore militant. The official said the nine were suspected of involvement in the stunning assault last Sunday, in which gunmen stormed an army checkpoint by the borders with Gaza and Israel, and killed 16 soldiers as they were breaking their daily fast for the holy month of Ramadan with a sunset meal. The attackers then commandeered an armored vehicle, which they later used to storm across the border into Israel where they were hit by an Israeli airstrike that killed at least six militants. Large swaths of northern Sinai have plunged into lawlessness following the ouster of Mubarak in last year's uprising, and weapons smuggled from Libya have found their way into militants' hands. The weapons and the security vacuum fueled the rise of Al-Qaeda-inspired militant groups which have staged several low-level cross-border attacks on Israel. Security officials estimate the number of militants in northern Sinai to some 1,500 but some Bebouin tribal leaders have put the number in the thousands. One prominent tribal chief, Awda Abu-Malhous, put it as high as 10,000. The military sent tanks and troops to the peninsula to combat the terror groups. However, witnesses say the offensive has been limited to a few raids on houses of suspected militants. Al-Ahram newspaper and other state-run papers reported Friday that 60 “terrorists" have been killed in airstrikes. However, medical officials say no bodies reached Al-Arish's only hospital. Officials said earlier that along with the offensive, Egypt is going after an elaborate network of underground tunnels used to smuggle weapons, militants and goods between Sinai and Gaza. Al-Ahram reported that 150 tunnels have been destroyed. Resident in the area said the tunnels targeted were not the most active ones. The weekend attack has rattled the Egyptian government, the military council and the country's Islamist President Mohammed Morsi, who fired the chief of intelligence in an apparent attempt to defuse public discontent. — AP