BANGKOK (AFP) - A grenade attack on demonstrators occupying the Thai prime minister's offices killed one person and wounded 29 Thursday, prompting angry protest leaders to vow a new march against the government. In the first fatal assault inside the Government House compound since the People's Alliance for Democracy (PAD) stormed it in August, unknown attackers fired the grenade into the compound before dawn Thursday, Bangkok police said. PAD chiefs accused the government of being behind the attack and called for massive protests against the current administration, which they allege is a corrupt proxy for ousted Prime Minister Thaksin Shinawatra. "The PAD will no longer tolerate daily brutal crackdowns by the government and cannot accept any type of Thaksin regime," the group said in a statement. "Therefore we have reached a consensus to call for a mass protest on Sunday November 23 at 0700 GMT to move to parliament to finally get rid of the proxy government and stop the tyrants." About 300 PAD supporters brought the dead man's body in the back of a pick-up truck to Bangkok's Metropolitan Police Headquarters to call for justice, a policeman there said, before taking the coffin to a nearby temple. The 48-year-old man died in hospital of shrapnel wounds, an emergency services spokeswoman said. Most of the 29 people injured have been discharged, she said, but two remain in a critical condition. Prime Minister Somchai Wongsawat, who is Thaksin's brother-in-law, immediately denied any involvement and vowed a swift police investigation into the incident. "It is not government policy to use force or violence," Somchai told reporters. "No one wants bloodshed or killing among Thais." Thailand has been gripped by political turmoil since May when the PAD began their rallies, but there was a respite for the six-day funeral of Princess Galyani, late sister of deeply-revered King Bhumibol Adulyadej. Chamlong Srimuang, a PAD founder, vowed to bring supporters to parliament on Sunday ahead of a joint session on Monday for a "last fight." "We have demonstrated for 180 days," he told reporters. "We will fight as best as we can and we hope we will win." Police refused to speculate on who was behind Thursday's attack, but General Jongrak Chutanont, deputy national police chief, said that the explosion was caused by a grenade fired from an M 79 launcher outside the compound. Police meanwhile have said the PAD's personal militia who guard the protest camp " known as the "Srivijaya Warriors" " are armed, and two people have been shot after rows near the occupied compound in central Bangkok.