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A roadside bomb exploded in a restive suburb of the Syrian capital as senior U.N. officials toured the area on Sunday, the latest incident in which the unarmed observer mission has nearly been caught up in the country's bloodshed.

No casualties were reported in the blast, which detonated about 150 meters (500 feet) away from visiting U.N. peacekeeping chief Herve Ladsous and Maj. Gen. Robert Mood, the chief of U.N. observers in Syria. Journalists accompanying the team also were nearby. The explosion blew off the front of a parked vehicle.

A U.N. observer team with more than 250 members now on the ground has failed to quell the bloodshed in Syria, although it says it has had a "calming effect" in certain areas. Meanwhile, on several occasions, the team has come close to being caught in an attack, although there is no conclusive proof that it has been targeted.

Earlier this month, a bomb targeting an army truck exploded seconds after a convoy carrying Mood went past in the country's south. Last week, a roadside bomb damaged the mission's cars in a northern town just minutes after witnesses said regime forces gunned down mourners at a funeral procession nearby.

It was not immediately clear what the target of Sunday's explosion was, but the damaged car was parked near a security checkpoint in the suburb of Douma. A security official at the checkpoint told the U.N. observers that gunmen had targeted two military buses in Douma earlier in the day, wounding more than 30 security agents.

"We obviously don't have the specifics about what happened here this morning," Mood said Sunday.

Ladsous gave a grim assessment of conditions for civilians in Douma, the scene of repeated clashes between security forces and rebels in recent months.

"The city (Douma) is completely paralyzed," Ladsous said. "There is still some fighting taking place. ... It's absolutely imperative that all parties exercise restraint and don't engage into any more fighting. It serves nothing."

Activists reported heavy shelling Sunday in the town of Soran in the central Hama province. The Britain-based Syrian Observatory for Human Rights called on the international observers to visit Soran and investigate reports of more than a dozen killed.

In Damascus, opposition groups reported fighting overnight between government forces and army defectors in the district of Kfar Souseh, a hotbed of dissent against President Bashar Assad's regime. The district is a high security area, housing the Foreign Ministry and several security and intelligence agencies. It has also been the scene of frequent anti-Assad demonstrations since the uprising began.

"Violent clashes broke out between rebel fighters and regime troops at a checkpoint in Kfar Souseh district," the Observatory said in a statement. Both the Observatory and another activist group, the Local Coordination Committees, said explosions and gunfire were also heard in several other neighborhoods of Damascus.

Syrian rebels claimed in an Internet statement that they carried out a sophisticated attack that killed top political and security officials meeting in the capital. The posting claimed those killed included Maj. Gen. Assef Shawkat, the deputy chief of staff for security affairs; Defense Minister Dawoud Rajha; Interior Minister Mohammad al-Shaar and former defense minister, Hassan Turkmani.

Several of those officials reported killed subsequently showed up in public to refute the claims. Al-Shaar denied them at a press conference. Turkmani was interviewed by state-run Syrian TV in his office and said the claims were "blatant lies."

Syrian officials rarely respond to statements issued by the opposition and their quick denials on Sunday were unusual.

The revolt against Assad's regime started in March 2011 with mostly peaceful protests calling for political change. The deadly government crackdown led many opposition supporters to take up arms. Now, the regime is facing an armed insurgency targeting government installations, soldiers and security forces.

In March, the U.N. said that 9,000 people had been killed. Hundreds more have died since.

Clashes in the heart of the Syrian capital have become more common recently but are still rare compared to other opposition strongholds in Syria that witness deadly violence almost daily.

A cease-fire that was supposed to start last month has never really taken hold, undermining the rest of international envoy Kofi Annan's plan, which is supposed to lead to talks to end the 15-month crisis.

World powers remain divided on how to end Syria's crisis. The U.S. and other Western and Arab nations have called for Assad to leave power, and the U.S. and European Union have placed increasingly stiff sanctions on Damascus. But with Russia and China blocking significant new U.N. punishments, U.S. officials are trying to get consensus among other allies about ways to promote Assad's ouster.

Also Sunday, an anti-Syrian cleric and his bodyguard were shot dead in neighboring Lebanon, where a spillover of Syria's conflict has inflamed tensions and triggered deadly sectarian fighting in recent days.

The two were on their way to a rally in a remote northern Sunni region when they were shot. The circumstances surrounding their deaths remain unclear but the state-run National News Agency said Sheik Ahmed Abdul-Wahid and his guard appeared to have been killed by soldiers after their convoy failed to stop at an army checkpoint.

The deaths could add to the tensions between pro and anti-Syrian groups in the region, and there were fears of clashes breaking out as the cleric's supporters blocked roads with burning tires in protest.

The Lebanese army issued a statement, saying it deeply regretted the incident and that a committee will investigate.

Clashes between pro- and anti-Syrian groups in the northern Lebanese city of Tripoli left eight people and dozens wounded this week.

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Karam reported from Beirut.