Saudi Arabia must "release immediately and unconditionally six Saudis" held for nearly a year in connection with a protest that only one of them attended, Amnesty International said on Friday.

The London-based rights group said five of the men were being held without trial in connection with Saudi Arabia's "Day of Rage" protest which was planned for March 11, 2011.

Four generals who had defected from the Syrian army arrived in Turkey Friday, Anatolia news agency reported, citing local Turkish sources.

The four were among some 10 high-ranking army officers stationed in cities including Damascus, Homs and Latakia, who crossed the border into Turkey's southern province of Hatay to join the Syrian rebels, the state-run Turkish agency said.

An Israeli air strike on the Gaza Strip killed the head of the Popular Resistance Committees militant group Friday, the movement said.

The PRC said General Secretary Zohair al-Qaisi was one of two Palestinians killed in the strike, along with fellow-member Mahmoud Halani, hours after Palestinians fired mortar rounds into Israel.

Tens of thousands demonstrated across Syria on Friday after the main weekly Muslim prayers, notably in northern Aleppo, with security forces opening fire on protesters in various regions, killing at least 82 people, activists said.

"There are 15 demonstrations taking place in the city of Aleppo and about 40 across the province," local activist Mohammed Halabi told Agence France Presse by telephone.

Thousands of Iraqis took to the streets of Baghdad and cities in the Shiite-majority south of the country on Friday to condemn Bahrain for crushing an uprising a year ago.

The protests, organized by Shiite cleric Moqtada al-Sadr, took place in a half-dozen cities in south Iraq with attendance ranging from dozens to several thousand, Agence France Presse reporters said.

Palestinian militants in the Gaza Strip fired two rockets into southern Israel Friday without causing any casualties or damage, a spokeswoman for the Israeli army said.

"Two rockets were fired toward the Eshkol area. They did not cause injuries or damage," the spokeswoman told Agence France Presse.

U.N.-Arab League envoy to Syria Kofi Annan is to visit Syrian refugee camps in Turkey after travelling to Syria over the weekend, a diplomat told Agence France Presse on Friday.

"Kofi Annan has expressed his wish to come soon to Turkey and we gave our consent," the diplomat said, on condition of anonymity.

Saudi Crown Prince Nayef bin Abdul Aziz, the kingdom's veteran internal security czar, arrived in the U.S. city of Cleveland on Friday for scheduled medical tests, the royal palace announced in Riyadh.

"The crown prince, (who is also) deputy prime minister and interior minister, arrived in Cleveland from Morocco for medical examinations that had been previously scheduled," the palace said in a brief statement carried by the official SPA news agency.

The leader of Syria's main opposition group rejected calls Friday by U.N. envoy Kofi Annan for dialogue with President Bashar Assad's government, saying they were pointless and unrealistic as the regime massacres its own people.

As the prospects for diplomacy faltered, Turkey's state-run television TRT said two Syrian generals and a colonel defected to Turkey on Thursday.

Syrian activists voiced growing fears on Friday of a major assault like the one that devastated the Homs neighborhood of Baba Amr, on the eve of a first visit by new international envoy Kofi Annan.

Troop reinforcements backed by tanks were massing in the northwestern province of Idlib, close to the Turkish border, in a bid to root out rebel fighters of the Free Syrian Army, activists and a human rights watchdog said.