Thai authorities say a pre-dawn blast has injured at least eight anti-government protesters in Bangkok near the site of a similar attack two days ago.

Sources in Bangkok say unidentified assailants on a motorcycle early Saturday threw a grenade at a checkpoint manned by protesters outside the prime minister's office compound.  Protesters led by the People's Alliance for Democracy have occupied the compound for nearly three months.

On Thursday, a grenade attack on the grounds of the compound killed one protester and injured 23 others.  No one has claimed responsibility for the blast, and protesters have refused to allow police to enter the compound to investigate the incident.  

PAD leaders blame the government for the attack and are organizing a mass rally on Sunday to protest what they say are the government's daily brutal crackdowns.  Prime Minister Somchai Wongsawat denies the accusations.

On Friday, Thailand's main public sector unions threatened to strike nationwide next week if the country's current administration does not step down.  The group of unions urged its nearly 200,000 workers to join an anti-government rally planned for Sunday in Bangkok.

Protesters have been calling for the administration to step down since they began occupying Thailand's Government House compound in late August.  They say the current administration is too close to deposed Prime Minister Thaksin Shinawatra.  

The standoff has paralyzed the government and led to fears it will plunge Thailand into economic chaos.

Some information for this report was provided by AFP and AP.