The Sinai-based jihadist group Ansar Bayt al-Maqdis claimed responsibility in a statement released on the Internet for the assassination of a senior Egyptian Interior Ministry official outside his home in Cairo.
On Wednesday, an army spokesman blamed the assassination, and another, also on Tuesday, of a policeman guarding a church, on the Muslim Brotherhood.
The jihadi group also claimed responsibility for an attack on a gas pipeline in Sinai.
The death of Gen. Muhammad Saeed, head of the technical office in the Interior ministry, suggested guerrillas were stepping up their campaign against the state.
Ansar Bayt al-Maqdis (“Supporters of Jerusalem”), which posted a video online this week of what it said was its fighters shooting down an Egyptian military helicopter with a surface to-air missile (SAM), is causing concern in Washington.
Meanwhile, Egypt will put an Australian, two Britons and a Dutchwoman on trial for aiding 16 Egyptians belonging to a "terrorist organisation", the public prosecutor said on Wednesday, describing the four as Al Jazeera correspondents.
Three of the Qatar-based television network's journalists - Peter Greste, an Australian; Mohamed Fahmy, a Canadian-Egyptian national; and Baher Mohamed - were detained in Cairo on Dec. 29 and remain in custody, Al Jazeera said.
The identities of the other foreigners mentioned by the prosecutor were not immediately clear.
In a statement, the prosecutor said the four had published "lies" that harmed the national interest and had supplied money, equipment and information to the 16 Egyptians. The foreigners were also accused of using unlicensed broadcasting equipment.
Al Jazeera’s Cairo offices have been closed since July 3, when security forces raided them hours after the army ousted president Mohamed Morsi.
Qatar was a strong financial backer of Egypt during Morsi’s year in power and the Gulf Arab state has vehemently criticized his overthrow and the ensuing crackdown on the Muslim Brotherhood.
Egypt’s Press Syndicate condemned the string of recent arrests and assaults on journalists, issuing a statement on Tuesday.
“Pitting citizens against journalists with false claims” could bring the country “back to the eras of deposed presidents Hosni Mubarak and Mohamed Morsi,” it said, according to Daily New Egypt.
The government has declared the Brotherhood a terrorist group and continued its crackdown on Tuesday, seizing the assets of 46 Brotherhood leaders, Ahram Online reported.
Separately, Special Envoy of the Middle East Quartet Tony Blair arrived in Cairo on Wednesday on a private jet to discuss regional issues with Egyptian officials.