Hotel used by U.N. observers rocked by explosion in Damascus, Syria's capital city

Updated at 9:14 a.m. ET

(CBS/AP) DAMASCUS, Syria - A bomb attached to a fuel truck exploded Wednesday outside a Damascus hotel where U.N. observers are staying, wounding at least three people, Syria's state TV reported.

The government controlled channel said the explosion took place near a parking lot used by the army command, which is about 300 yards away.

Syrian Deputy Foreign Minister Faisal Mekdad toured the area of the blast and said none of the U.N. staff was hurt. The explosion occurred as U.N. humanitarian chief Valerie Amos was in the Syrian capital but her team is believed to be staying at a different hotel.

CBS News' George Baghdadi reports the area near the blast was quiet following the explosion. There had been reports of clashes after the blast, but Baghdadi saw no sign of violence.

Mekdad called the explosion a "terrorist act" meant to "destabilize" the country.

The lot where the explosion occurred is near the Dama Rose Hotel, popular with the U.N. observers in Syria.

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The hotel was slightly damaged in the blast, with some of its windows shattered. A Labor Union building across from the hotel was also damaged and black smoke was seen billowing into the sky before the fire was extinguished.

Badghdadi says there are many foreign embassies in the up-market neighborhood where the Dama Rose is located, but there were no reports of damage to any other buildings.

CBS News correspondent Clarissa Ward reports that Wednesday's was the third explosion to hit Damascus in just four days. A rebel group claimed responsibility for the attack, saying it was aimed at the military compound nearby.

While the blast did not actually hit any members of the Syrian regime, it was further evidence that the rebel forces are increasingly able to bring the fight directly into the heart of the capital city - Assad's stronghold.

Opposition activists reported heavy fighting in other areas of the capital on Wednesday, saying tanks were shelling some neighborhoods and there were exchanges of gunfire near the prime minister's office, and behind the Iranian Embassy.

Several fire engines arrived shortly after the morning blast to fight the blaze. The fire was extinguished less than an hour after the explosion.

U.N. officials in Damascus had no immediate comment when contacted by the AP.

"This is a criminal act that shows what kind of attacks Syria is being subjected to," Mekdad told reporters at the scene. "Such explosions will not affect Syria."

"I confirm that we are with the U.N. and we will do all we can to guarantee their protection so that they carry out their role," he added.

Damascus has been hit by a wave of explosions in the past months and clashes between government troops and rebels have also recently reached the capital, which had been relatively quiet since an uprising against President Bashar Assad's regime started in March last year.

Activists say more than 20,000 people have been killed since then, and the conflict has morphed into a full-out civil war.

"Those who carry out such terrorist attacks are destroying their country in order to get some pounds," shouted Ali Mohammed Ismail, 48, who said he happened to be in the area when the explosion occurred.