A top Jordanian Salafist leader said on Tuesday eight Sunni jihadists have been arrested as they tried to cross the border into neighboring Syria to fight President Bashar Assad's forces.

"The Jordanian authorities have recently arrested eight jihadists as they attempted to go to Syria for jihad. They are currently in the Zarqa prison waiting for prosecutors to charge them," Abed Shehadeh, known as Abu Mohammad Tahawi, told Agence France Presse.

Advance team leader Colonel Ahmed Himmiche acknowledged on Tuesday that a hard-won U.N. military observer mission to oversee a Syria ceasefire will be "difficult."

"We need to move forward little step by little step," the Moroccan officer told reporters.

Some 1,200 Palestinian prisoners held in Israeli jails have begun a hunger strike and another 2,300 are refusing food for one day, a spokeswoman for the Israel Prisons Service (IPS) said on Tuesday.

"In the framework of (Palestinian) Prisoners' Day, around 2,300 security prisoners said they were refusing their daily meals, and around 1,200 prisoners said they were starting a hunger strike," IPS spokeswoman Sivan Weizman told Agence France Presse.

A suspected U.S. drone strike in Yemen's southeastern Shabwa province has killed five Al-Qaida-affiliated militants, a local government official said on Tuesday.

Speaking on condition of anonymity, the official said a "U.S. drone" targeted the five men late on Monday in Shabwa, a mostly lawless region of Yemen where the extremist group has expanded its presence.

Syrian regime forces killed at least two civilians on Tuesday, as they kept up their bombardments of protest centers despite a warning by Washington that it is already discussing options in case a U.N.-backed peace plan collapses.

An advance team of U.N. military observers arrived in Damascus on Sunday to oversee a shaky ceasefire, but dozens of people -- troops as well as civilians -- have been killed since it went into force on Thursday, monitors said.

Iran will respond with force to any threats to its territorial integrity, President Mahmoud Ahmadinejad said on Tuesday, adding that it would prefer to cooperate with its Arab neighbors to maintain security in the Gulf.

"The armed forces and the army will inflict heavy regret and shame in case of any aggression against Iranian lands and interests," Ahmadinejad told military commanders and personnel on the occasion of Iran's annual Army Day.

Iran's foreign ministry on Monday summoned the Saudi ambassador to protest over Riyadh's treatment of Iranian nationals jailed in the kingdom, the official IRNA news agency reported.

Ministry officials questioned the ambassador over "worrisome" reports on the treatment of Iranian nationals jailed in the city of Dammam, capital of the Eastern Province that is home to most of the kingdom's Shiite minority.

A U.N.-Arab League peace plan for Syria has only a three percent chance of working, the emir of Qatar said on a visit to Rome Monday, as a U.N.-backed ceasefire was marred by ongoing violence.

Sheikh Hamad bin Khalifa al-Thani told a press conference that the chances for success "are no higher than three percent", and that the Syrian people should not be supported through peaceful means but "with arms".

A German shipping firm on Monday dismissed reports one of its vessels was carrying Iranian arms bound for Syria in violation of EU sanctions against the regime of President Bashar al-Assad.

Respected news weekly Der Spiegel reported at the weekend that the ship, the Atlantic Cruiser, owned by German firm Bockstiegel but chartered by a Ukrainian firm, had been stopped on the high seas with Iranian weapons on board.

The United States warned Monday that heightened violence in Syria threatens the sending of a full U.N. ceasefire observer mission as it voiced fear that a ceasefire is "eroding."

The U.S. ambassador to the United Nations, Susan Rice, said new attacks by government forces "call into question the wisdom and viability" of sending the full 200 international monitors.