BANGKOK, Feb. 26 (Xinhuanet) -- A blast rocked a mass rally site at Sanam Luang, Royal Palace, here at 8:00 p.m. (1300 GMT) Sunday as thousands of protesters gathered to demand the caretaker Prime Minister Thaksin Shinawatra to step down.

    The explosion went off on an iTV transmission car parked at the center part of the square, sparking flames in surrounding areas, reported The Nation television.

    A broadcasting stage nearby has been on fire and black smoke was seen gutting out of the inflamed car.

    Police has arrived to cordon off the explosion site and evacuate the mass. The flames have been put under control and no casualties have been reported so far, said the Thairath website.

    The rally, which has started from Sunday noon involving tens of thousands of protesters, is still going on.

    The anti-government demonstration, the third one in a month, is apparent the largest despite the government's announcement to dissolve parliament and hold snap elections on April 2 to defuse escalating political tension.  Enditem