Ahmed Selim reports from Arish on recent turmoil in Sinai Security on Egypt's eastern border has been tightened following a spate of incidents, including attacks on police checkpoints, gas pipelines and police stations. The most bloody attack was on Qism Thani -- a police station in Arish -- that left six people dead; the most recent on a police station close to border marker 79. Masked men carrying black flags and using four wheel drives as transport are behind the attacks. Security forces have so far captured 20 suspects and killed at least one. They have uncovered an arms cache and are currently following leads that may result in more arrests. Last week's Israeli incursion across the border that left five Egyptian soldiers dead has added to tensions in the area, prompting the Supreme Council of the Armed Forces (SCAF) to hold meetings with local inhabitants. Bedouin tribesmen, who proved crucial in tracking down members of a ring of Islamist militants, have promised the SCAF more help in the future. In return the SCAF has formed two committees, one in North Sinai and one in South Sinai, to examine ways to meet outstanding demands from the local population. But who are the men with black flags? And how does the government plan to defeat them? Security experts say that the black flags are a symbol of vengeance against those whom Jihadists deem to have deviated from the righteous path. Preliminary investigations suggest the perpetrators of the attacks were prisoners being held for religiously-motivated violence who escaped from Egyptian prisons during the 25 January Revolution. A North Sinai security source, speaking on condition of anonymity, said that investigators believe that nearly half of the attackers have now been detained. Egyptian police and army forces are closely monitoring the borders with Rafah to ensure that remaining suspects do not escape to Gaza through the tunnels. Sinai is sparsely populated and the local population can easily spot outsiders. "Any stranger who appears in this part of the peninsula is immediately identified by the locals," the source said. He added that Bedouin trackers are helping the authorities in their investigations in remote mountain areas. "Most of those who have been arrested belong to extremist groups. They come from various governorates in Egypt, including Sohag, Qalioubiya, Suez and Sinai," the source stated. The authorities seem to be gaining the upper hand in the confrontation with the jihadists. Security has been tightened near Rafah and security forces are manning roadblocks on major and secondary roads, while the Bedouin have been helping identify any unusual movement in the desert. The first breakthrough in the investigation came when suspects arrested in a police raid began telling investigators about their operations. Security officials believe they now have enough leads in the case to capture the remaining suspects. They are particularly pleased with the outcome of their investigation into an attack on Al-Dohaysha in Sinai. Leads in the case pointed to a house in Arish where five militants were arrested, including a Palestinian member of Islamic Jihad. One of the men inside the house, identified by the police as Salem, 36, was a mechanic from Suez. He fired at the police and was shot dead. His accomplices then surrendered. Police found three automatic rifles, four grenades, 11 rifle cartridges and 330 rounds of ammunition in the house, as well as a laptop and a printer. In the same raid a 24-year-old Palestinian member of Islamic Jihad in Gaza -- identified only as Yasser -- was arrested. He told investigators that he had travelled to Egypt repeatedly through cross-border tunnels. Mohamed Gomaa Salah, 31, a labourer from Qalioubiya; Hossam Abdel-Radi, 23, from Sohag; and Omar, 25, a college graduate from Alexandria, were also detained. Omar told investigators that he embraced militant Islam a few years ago and believed in violence as a way to secure religious emancipation. Another suspect, identified as El-Mallah, is alleged to have travelled frequently between governorates seeking out like-minded jihadists. He arrived in Arish after the revolution and hooked up with several jihadists. Together they planned attacks on police stations and gas pipelines. El-Mallah, investigators say, is a former prisoner of Abu Zaabal prison. He was wounded during the attack on the police station. Yasser told investigators that he received training in Sinai and Gaza. He took part in the attack on the police station and was supplying the group with weapons and explosives. Hossam told investigators that he arrived in Arish six months ago to work closely with other jihadists. He was responsible for procuring weapons and took part in the attack on the police station. He described the investigators as "infidels" and denounced all security personnel as "apostates". The authorities subsequently raided a safe house in Zarea, west of Arish, where they found gun-manufacturing machinery in an underground room. A man in his 20s surrendered and then revealed the whereabouts of two accomplices. Investigators found explosives, grenades and a laptop containing information on bomb making in the house. They also found a sniper rifle stolen from the police in an earlier attack. The detained men confessed to involvement in the police station attack and in sabotaging natural gas facilities. They told investigators that they collected unexploded ordnance to manufacture new bombs. Some of their knowledge of bomb making came from the Internet and the rest came from Yasser, the Palestinian member of the group. Ayman Hammad, an officer in North Sinai Security Investigation Department, was behind another breakthrough. He spotted a man trying to conceal an automatic rifle in the folds of his clothes in an area just south of Arish. The man, who was also found to be in possession of grenades, admitted belonging to the jihadist outfit. In another incident, what looked like a roadside bomb was placed close to the North Sinai Security Department. Bomb experts discovered the explosive device to be a decoy, an attempt to waste police time and frighten the public. Attacks followed in which roadblocks in Arish and other areas were fired at. No casualties were reported. North Sinai Security chief Saleh Al-Masri says the security campaign is still underway and that the authorities are receiving valuable help from tribesmen in Sinai. A meeting between locals and members of the SCAF at the Armed Forces Club in Arish was attended by Major General Ibrahim Nesuhi, Major General Mohamed Farid, commander of the second Field Army, Major General Ahmed Youssef Abdel-Nabi, commander of the Border Guard Corps and Major General Ali Hafzi, a former governor of North Sinai. Nesuhi offered the SCAF's condolences to families of those who had died in recent events. He said that the SCAF is intent on bringing law and order, as well as development and prosperity, to Sinai.