The Thai police, on Saturday, fired teargas shells and detained dozens of demonstrators as clashes erupted at the first major street protests against Prime Minister Yingluck Shinawatra’s government. About 17,000 police were deployed for the rally in Bangkok’s historic district, which was organised by the royalist group Pitak Siam, a relatively new force in the kingdom’s fractured political scene.

“I promise that we will topple this government,” the movement’s head, retired general Boonlert Kaewprasit, declared from the rally stage.

The authorities expected tens of thousands of people to attend the demo, which comes about two-and-a-half years after dozens of people died in a military crackdown on opposition protests in the heart of the capital.

By early afternoon police estimated that about 12,000 people had turned out. Police said they fired teargas at a group of protesters who removed barbed wire and barriers blocking their route in front of a UN building close to the main rally site. About 100 protesters were detained.