The Palestinian presidency hopes U.S. President Barack Obama's forthcoming visit will mark the beginning of a new U.S. policy in the region, a spokesman said on Wednesday.

"President Mahmoud Abbas welcomes the visit of U.S. President Barack Obama to Palestine," Nabil Abu Rudeina, spokesman for the Palestinian presidency told Agence France Presse.

Prominent Tunisian opposition leader Chokri Belaid was shot dead on Wednesday, sparking deadly protests, attacks on offices of the ruling Islamist Ennahda party, and the pledge of a new government of technocrats.

Furious protesters built barricades in central Tunis and clashed with police, and four opposition groups including Belaid's Popular Front bloc said they were pulling out of the national assembly.

Bored at home and eager to join their older brothers and fathers on the frontline against President Bashar Assad's army, Syrian teenagers are joining the rebel cause, oblivious to international laws prohibiting child combatants.

"When they arrive here, they are children. By the time they leave, they are killing machines," said Abdel Razzaq, a 38-year-old former army sergeant who trains the boys.

At least 12 members of Syria's security forces were killed in two suicide car bombings targeting a military intelligence headquarters in the south-central city of Palmyra on Wednesday, a watchdog said.

The Syrian Observatory for Human Rights said that more than 20 troops were also wounded, some in critical condition, after the simultaneous attacks against the intelligence branch and a nearby security building.

Tehran's ex-prosecutor and controversial ally of President Mahmoud Ahmadinejad was released from the notorious Evin prison on Wednesday after almost two days in detention, Iranian media reported.

The reports did not elaborate on the circumstances of Saeed Mortazavi's release nor of his arrest on Monday night when he was sent to Evin, where many political prisoners and journalists have been imprisoned over years on his orders.

U.S. Defense Secretary Leon Panetta spoke by phone with his Egyptian counterpart on Tuesday to hear an update on the tense political situation in Cairo and the "role" of the army amid recent street demonstrations, a Pentagon spokesman said.

Defense minister and military chief General Abdel Fattah al-Sissi, who has warned the state could collapse in the face of political upheaval, voiced support for maintaining strong security ties with Washington and reassured Panetta that the armed forces remained committed to his country's peace treaty with Israel, spokesman George Little said in a statement.

Israel has deployed a third Iron Dome missile defense battery to the north of the country a few days after carrying out an air strike inside neighboring Syria, Israeli media said on Tuesday.

"The deployment of several Iron Dome batteries in the north of the country comes as part of the setting up of the system," an army spokesman was quoted as saying.

President Barack Obama plans to soon make his first trip to Israel as U.S. leader to confer on the Iranian nuclear showdown and to soothe his delicate relationship with Prime Minister Benjamin Netanyahu.

The White House said Tuesday that Obama also plans to stop to talk to Palestinian leaders in the West Bank and to travel to Jordan on his trip, which will bring him close to the turmoil threatening to tear Syria apart.

The possible downfall of Syrian President Bashar Assad could open new and dangerous fronts for Israel, even if it weakens Hizbullah, experts say.

While nobody can predict when or how Assad's regime could crumble, such a scenario "would dramatically affect Israel," a senior Israeli security official speaking on condition of anonymity told Agence France Presse.

The Syrian National Council, the main component of the opposition National Coalition, on Tuesday rejected the possibility of holding any talks with the regime as offered by the head of the umbrella group.

"The Syrian National Council has already told the people of the revolution of its commitment to its principles and objectives... the overthrow of the Syrian regime and all its parts, the rejection of any dialogue with it, and the protection of the revolution so that it does not become hostage to any international commitments," it said in a statement.