GAZA CITY — Fatah and Hamas have stepped up operations following renewed violence between the rival militia groups.

Palestinian sources said both movements have increased security around key members in the Gaza Strip as well as parts of the West Bank. They said operatives have been ordered to search for targets.

On Thursday, Fatah and Hamas gunmen clashed in Gaza City as General Intelligence officers arrested a commander of the Hamas-aligned Popular Resistance Committees, Hisham Mukhaimar. In the shootout, three GI agents, led by a Fatah commander, were injured, Middle East Newsline reported.

Hours later, Hamas abducted a GI officer, identified as Maj. Mohammed Abu Siyam. The Hamas PRC has warned of unspecified consequences unless the PA agency released Mukhaimar.

On Wednesday, a Hamas commander was killed by unidentified gunmen in the southern Gaza town of Khan Yunis. Bassam Al Fara, 32, also served as a judge in the Islamic civil court in the Palestinian Authority.

"He was a key Hamas military commander in the Khan Yunis region," a Palestinian source said.

The killing took place about 48 hours after suspected Hamas gunmen killed three children of a senior PA intelligence official. The official was not in the targeted car that brought the children to school in Gaza City on Dec. 11.

Neither group has claimed responsibility for the killings. But each militia has blamed the other for the deaths of its members.

"Once again, the death squad, which was created using suspect elements affiliated with the [Fatah-aligned] Preventive Security Apparatus, has come to assassinate an Al Kassam commander and a religious scholar," Hamas's military wing said in a statement.

Palestinian sources said Hamas and particularly Fara's family would seek to avenge the killing. The Fara clan is one of the biggest in Khan Yunis and engages in arms smuggling and property.

The renewal of the Fatah-Hamas militia war has led PA Prime Minister Ismail Haniyeh to cut short his foreign tour. Haniyeh plans to return on Thursday to the Gaza Strip, reducing his stay abroad by more than two weeks.

"We condemn in the strongest terms these criminal actions organized by a putschist element within Fatah, which is inciting trouble by organizing armed demonstrations by killing and by using criminal methods against Hamas members," Hamas spokesman Ismail Radwan told a news conference in Gaza City. "We will not remain with our arms crossed in the face of trying to torpedo the national boat."