The government alleges the Brotherhood has been behind the militant campaign from the start, accusing its leaders of working with militants to launch the insurgency. In December, it declared the Brotherhood a terrorist organization. The Brotherhood, which officially renounced violence in the 1970s, denies the accusation and calls it a pretext to wipe out the government's top political rival, which won a string of elections after Mubarak's fall.
Egypt's security agencies say they have amassed evidence of the Brotherhood's role. But so far it has largely not been made public or been put through judicial scrutiny. Instead, their purported evidence has come out in a flow of leaks to the Egyptian press by anonymous officials — making its veracity impossible to assess independently.
In December, for example, officials in the prosecutors' office leaked to the Egyptian press the purported confessions of Mohammed el-Zawahri, the brother of al-Qaida's leader who is himself a prominent figure in extremist circles and was a strong supporter of Morsi's presidency. He was arrested soon after Morsi's ouster.
According to the leaks, he told interrogators that the Brotherhood's deputy leader Khairat el-Shater gave him millions of dollars to buy weapons from Libya for Sinai militants and demanded they attack the military and government institutions.
Officials also have spoken of recorded telephone calls between Brotherhood leaders and militants. They claim the Brotherhood had access to police files during Morsi's presidency and passed information to militants, helping them assassinate security officials. Among them was a top Interior Ministry official in charge of investigating the Brotherhood who was gunned down outside his home late last year.
During Morsi's presidency, he formed a political alliance with radicals, including former members of militant groups that fought a bloody insurgency against the government in the 1990s. Also while president, Morsi sent ultraconservative Islamist envoys to negotiate with Sinai militants to stop attacks in return for a halt to military operations against them. Morsi's allies represented the contacts as aimed at finding a peaceful solution to Sinai violence, but security agencies allege the contacts built the alliance with jihadis.
In the days just before the coup and in the weeks after, some of the top leaders of past militant movements appeared on the stage of the main pro-Morsi protest camp in Cairo, outside the Rabaah al-Adawiya mosque. Among them were Rifai Taha, who was once allied to al-Qaida leader Osama bin Laden in Afghanistan, and two brothers, Tareq and Abboud el-Zomor, who spent years in prison for masterminding the assassination of former Egyptian President Anwar Sadat in 1981.
One former militant leader, Assem Abdel-Maged, openly threatened violence against Morsi's opponents from the stage at Rabaah, telling the crowd, "We will have to press the knife now."
Regardless of the truth of the government accusations, experts warn that the crackdown is pushing Islamists into militant violence and creating a pool of potential recruits for Islamic militant groups.
Aside from the well-planned attacks claimed by Ansar Beit al-Maqdis, there have been frequent less sophisticated bombings, including explosives planted outside police stations or on roadsides targeting police patrols.
Last week, a new group calling itself Ajnad Misr, Arabic for Egypt's Soldiers, claimed responsibility for several such bombings, including one on Jan. 24 that hit police just as they returned from clashes with Morsi supporters. To experts, that suggests the group is drawing recruits from the ranks of Islamist protesters.
"The emergence of Ajnad Misr testifies to how a large number of Islamists who had been adopting peaceful means are now resorting to violence since there is no use to peaceful protest," said Ismail Alexandrani, an Egyptian expert in Islamic militancy.
AP correspondent Maggie Michael contributed to this report.
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