Mr Sondhi Limthongkul accused the government of having a direct hand in the firing of the grenade in the early hours of Thursday into the Government House compound that has been occupied by the People's Alliance for Democracy (PAD) since August.

'The PAD can no longer tolerate this murderous government that kills its people daily and cruelly,' Mr Sondhi said, reading out a statement after an emergency meeting of the street movement's inner circle.

'The PAD have therefore decided to call the biggest rally ever on November 23 at 2pm to march to parliament to end the puppet government,' he said. The statement was broadcast live on the PAD's own radio and satellite television channels.

Besides the dead man, identified as a 48-year-old with shrapnel wounds to the chest, 23 people were wounded in the grenade blast, the most serious assault on the three month sit-in.

Police have little information about the incident because PAD sentries have barred them from entry to the barricaded Government House compound.

The PAD is a loose coalition of royalist businessmen and academics trying to prevent former leader Thaksin Shinawatra returning to power following his removal in a 2006 coup.

Its campaign, which started in late 2005 and contributed heavily to the coup, has paralysed government decision-making and exacerbated the threat of recession in Thailand as its export-oriented economy takes a hit from a global slowdown.

Thailand's political temperature has been relatively calm for the last two weeks, with many people in both the pro- and anti-government camps turning their attention to last weekend's high-profile cremation of the king's elder sister.

However, analysts always said the lull would almost certainly be only temporary, and so Thursday's attack comes as no surprise. Last month, one renegade old general threatened to launch daily bomb attacks against the PAD. -- REUTERS