Russia urged its Middle East ally Syria on Tuesday to refrain from using chemical weapons despite its threat to unleash the previously unreported arsenal in case of a foreign attack.

The foreign ministry said it "would like to underline that Syria joined" a Geneva protocol on the non-use of such weapons and "presumes that the Syrian authorities will continue to rigorously abide by its assumed international obligations".

More than 10,000 Iraqis have fled Syria to return home since Wednesday fearing for their lives, the U.N. refugee agency said.

"Many of the returnees have expressed their fear regarding the ongoing risks to their safety in Iraq, but said they had little choice, given the security threats in Syria," UNHCR spokeswoman Melissa Fleming said in Geneva on Tuesday.

Renowned Syrian sculptor Wael Qastoun has been tortured to death in the flashpoint central of city of Homs, an artists' association said on Tuesday.

A statement released by the Syrian Coalition of Artists for Freedom said Qastoun "died under torture."

Syrian government troops attacked the Qadam and Assali districts of Damascus on Tuesday, two of the last pockets of rebel-held territory in the city, a watchdog said.

"Syrian regime forces have attacked the Qadam and Assali districts, launching a wave of raids and arrests," the Britain-based Syrian Observatory for Human Rights said.

Syrian rebel forces are stretching the Syria army nationwide, grabbing border posts and countryside regions as they challenge the regime in its symbolic power centers of Damascus and Aleppo, experts say.

An attack in the heart of Damascus last week, claimed by the rebel Free Syrian Army, killed four senior regime members and forced the government to redeploy troops to the capital, leaving gaps elsewhere that the rebels can exploit.

A top Iranian military official warned on Tuesday that Syria's allies "will not allow regime change" and would land "decisive blows" on Damascus's enemies if they entered the growing conflict.

"The Syrian people and the friends of Syria will not allow regime change," Brigadier General Masoud Jazayeri, the deputy chief of Iran's joint armed forces, was quoted as saying on the official website of the Revolutionary Guards, sepahnews.com.

An international media watchdog on Tuesday urged the United Arab Emirates to release a group of Internet activists held on charges of "opposing the constitution."

The Gulf state had arrested 18 "campaigners and rights activists" between July 16 and 19, said Reporters Without Borders (RSF). Only one of them has been released.

Greece is preparing to close its embassy in Damascus, the foreign ministry said Tuesday, after last week warning about the deteriorating security situation there.

"The foreign ministry is closely observing and constantly evaluating the state of security and has put under way the closure of the embassy of Greece in Damascus," it said in a statement.

The trial of Iraq's fugitive Vice President Tareq al-Hashemi, accused of running death squads, was postponed Tuesday after defense requests to call President Jalal Talabani to testify were again denied.

Hashemi, last known to be in Turkey, is being tried in absentia along with several of his bodyguards in a case which when initially filed in December as U.S. troops were pulling out worsened a brewing political crisis.

Syria has named General Ali Mamlouk as the new head of its national security office and General Rustom Ghazali as the new chief of political security, in a shakeup of the security services after a bombing killed four top regime figures last week, a security source told Agence France Presse on Tuesday.

"General Ali Mamlouk, who was head of state security, is becoming the head of the bureau of national security, with the rank of minister, overseeing the entire security apparatus," the source said.