Updated

An Egyptian militant group claimed responsibility Sunday for twin suicide bombings that targeted a military checkpoint and a tourist bus, killing at least one solider and wounding nine in the southern Sinai Peninsula two days earlier.

In a statement posted on militant websites, the Al Qaeda inspired group Champions of Jerusalem warned the Egyptian army: "We will not rest until we achieve retribution for the blood and honor of the Muslims."

The group has been behind the deadliest attacks against military and police installations in Egypt since a spike in violence last summer following the military overthrow of Islamist President Mohammed Morsi. Another new group, known as Egypt's Soldiers has claimed responsibility for several smaller bombings targeting individual police officers.

The violent campaign was at first concentrated in the lawless northern Sinai, where a slew of militant groups have found refuge since the Egypt's 2011 uprising. But the attacks moved closer to the capital as security forces intensified a security crackdown on supporters of the ousted president, leaving hundreds killed and thousands behind bars.

Security officials fear the attacks on troops would intensify ahead of the presidential elections, scheduled for later this month, where Abdel-Fattah el-Sissi, the former military chief who oversaw Morsi's ouster, is the front-runner.

Friday witnessed a series of attacks in Cairo and southern Sinai, a tourist destination that has seen so far four suicide bombings since Morsi's ouster, including one in February that killed three South Korean tourists in the bus they were riding. On Friday, a bomber blew himself up near a tourist bus carrying Egyptian workers in el-Tor, in southern Sinai, killing only himself and wounding four, security officials said. The health ministry initially said a civilian was killed. It was not clear if the bomber was aiming to target foreign tourists, or the Egyptian workers. So far, besides the South Koreans, the group has mainly targeted security forces, and has largely stayed clear from targeting Egyptian civilians.

On the same day, another attacker blew himself up at an army checkpoint also in el-Tor, killing a soldier and himself, and wounding five others, the officials said. Initially, a civilian was also believed to have been killed in the attack. In Cairo, a homemade bomb planted at a police post killed an officer, while a car used usually by military officers exploded, killing a civilian. No one claimed responsibility for these two attacks.

In its statement, the group urged the Egyptian people to "rebel against this oppressive and tyrannical regime" and to not resort only to peaceful opposition.

Also on Sunday, security officials said masked gunmen shot dead a retired intelligence officer in el-Arish, the capital of northern Sinai, after he dropped his children at school. The retired officer was heading a local prominent charity organization, and the motive for his killing was not immediately clear.

The security officials were speaking on condition of anonymity because they were not authorized to speak to the media.