More than 16,500 people have been killed in violence since an uprising against President Bashar Assad broke out in March last year, the Syrian Observatory for Human Rights said on Monday.

Iran on Monday said it was readying ballistic missile war games simulating a counter-attack against U.S. or Israeli targets in the region in the event of air strikes on its nuclear facilities.

The three-day drill in Iran's central desert region was starting days after the European Union and the United States imposed severe new sanctions, and on the eve of another round of negotiations with world powers seeking to curb Tehran's nuclear ambitions.

The Syrian army kept up its bombardment of rebel neighborhoods of the central city of Homs on Monday, activists said, after 79 people were killed in violence across the country the previous day.

Thirty-eight civilians, six of them children, were among Sunday's dead, the Syrian Observatory for Human Rights said. The violence also claimed the lives of 13 rebel fighters and 28 government troops, the Britain-based watchdog added.

Yemeni security forces have foiled a plot to carry out 10 suicide bombings against government buildings in the capital Sanaa, the defense ministry's news website reported on Monday.

A wave of arrests targeting a suspected al-Qaida cell held responsible for a May attack that killed more than 100 soldiers in the capital netted the 10 militants charged with carrying out the bombings, the 26sep.net website quoted "informed sources" as saying.

Syria-based rebel fighters and activists said they would boycott an opposition meeting in Cairo on Monday, denouncing it as a "conspiracy" that served the policy goals of Damascus allies Moscow and Tehran.

The two-day meeting, to be attended by the main exiled opposition bloc, the Syrian National Council, and other smaller groups, is intended to forge a common vision for a political transition in Syria after 16 months of bloodshed.

A Saudi diplomat abducted by al-Qaida in Yemen's south has made a new appeal to King Abdullah to secure his release by meeting the demands of his captors, according to a video posted on jihadist forums.

"Why are you refusing to free the prisoners?" Abdullah al-Khalidi asked the Saudi monarch in the video posted Sunday and published hours later by SITE Intelligence Group.

Violence across Syria killed at least 43 people on Sunday, 36 of them civilians caught in fierce fighting between troops and armed insurgents.

Sunday's highest concentration of deaths was in the eastern province of Deir Ezzor where nine civilians and three rebels were reportedly killed.

Jordan's King Abdullah II on Sunday called on opposition parties, particularly the Islamists, to take part in general elections later this year after they threatened to boycott the polls.

A criminal court judge was among three people killed in gun and bomb attacks north of the Iraqi capital on Sunday, security and medical officials said, in the latest in a spike in nationwide unrest.

In the restive city of Mosul, gunmen shot dead Judge Abdul Latif Mohammed while he was driving home, said police First Lieutenant Mohammed al-Juburi and Dr Mahmud Haddad in Mosul's main hospital.

Iran's Revolutionary Guards announced they are to fire ballistic and other missiles at desert targets during three days of war games starting Monday in a warning to threats of military action by Israel and the United States.

"Long-, medium- and short-range surface-to-surface missiles will be fired from different locations in Iran... at replica airbases like those used by out-of-region military forces," the head of the Guards aerospace division in charge of missile systems, Brigadier General Amir Ali Hajizadeh, said.