Police fired tear gas at a group of anti-government protesters as they were on the way to the rally site at the Royal Plaza on Saturday morning.
Police decided to fire the tear gas after the demonstrators tried to break through barricades at Makkawan bridge on Ratchadamnoen Avenue, TNN reported.
No injuries were reported from the clash, TNN siad.
The government did not allow them to go to the rally site at the Royal Plaza from Makkawan, where security authorities set up a barricade to control the Pitak Siam protest led by retired Gen Boonlert Kaewprasit. But the protesters ignored the ban, prompting anti-riot police to use tear gas.
Gen Boonlert was leading another group of protesters to the rally site from another entrance at the Royal Plaza.
He reiterated on Saturday that he could draw 1 million protesters and also promised a peaceful rally to oust the government.