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An explosive planted under an army vehicle exploded in the Syrian capital Saturday, damaging nine cars, while activists said Syrian forces were combing nearby areas for opponents of the regime.

The blast early Saturday shook a downtown Damascus neighborhood near a military food cooperative, destroyed nine cars and left a crater in the street, according to a reporter from The Associated Press who visited the scene.

Such explosions have become frequent as Syria's uprising against President Bashar Assad grows increasingly militarized. Numerous blasts have targeted the capital and other major cities where the regime's control is at its strongest.

Many in the opposition have taken up arms since protesters first took to the street in March 2011, prompting a government crackdown. The U.N. says more than 9,000 people have been killed.

No one immediately claimed responsibility for the blast.

Earlier this week, attacks on a government security compound and the country's central bank killed nine and injured 100.

On the outskirts of the city, tanks and troops combed through fields near the Barzeh neighborhood in the northeast as well as an area near Hamouriya in the east, activist Omar Hamzeh said via Skype.

"They are moving through the fields and firing anti-aircraft guns," he said, adding that the regime was probably looking to arrest activists. "The rural areas around there have been very active in protests against the regime."

The Britain-based Syrian Observatory for Human Rights also reported army raids in Barzeh.

Activist claims could not be independently verified. The Syrian government prevents most media from working freely in the country.

World powers remain divided on how to stop Syria's crisis, though all have fallen in behind a plan put forward by former U.N. Secretary General Kofi Annan that seeks a cease-fire in order for all sides to engage in political dialogue.

But the truce that was to begin on April 12 has never really taken hold, with regime forces continuing to shell opposition areas and shoot at protesters. Security forces killed one teenager following a protests in the northern city of Aleppo on Friday.

Armed rebels have kept up attacks on military checkpoints and convoys.

A spokesman for Annan, however, said Friday the international envoy believes his peace plan for Syrian remains "on track" — a day after the Obama administration offered a far bleaker view, saying the plan might be doomed.

A U.N. team of up to 300 members is to monitor compliance with a truce. U.N. peacekeeping chief Herve Ladsous said about 40 U.N. observers are on the ground in Syria and that the force will grow to 65 by Sunday.

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Associated Press writer Albert Aji contributed reporting from Damascus, Syria.