Police say six street cleaners have been wounded by a small explosion at an anti-government protest site in Thailand's capital.

Police Maj. Nopparuj Jitman says the explosion in central Bangkok was caused by an improvised bomb or a giant firecracker.

He says the cleaners from the city hall were changing tree pots at a street isle near the rally site when the blast went off before noon Monday.

The protesters want caretaker Prime Minister Yingluck Shinawatra to step down to make way for an interim appointed government to implement what they say are necessary reforms to fight corruption. They've been protesting since November and have battled police on several occasions.

At least 10 people have been killed and scores hospitalized during the unrest.