Thailand's election authority called Thursday for July polls to be postponed after three people were killed in a grenade and gun attack on opposition protesters in Bangkok, stoking fears of spiralling violence.

The latest wave of bloodshed comes as demonstrators push for the appointment of an unelected premier in a move that has infuriated government supporters.

The dismissal of prime minister Yingluck Shinawatra from office last week in a controversial court ruling has sent tensions soaring in the Southeast Asian nation, which has endured years of political turmoil.

Her "Red Shirt" supporters have warned of the threat of civil war if power is handed to an unelected leader.

Unknown assailants fired two grenades into a rally camp early Thursday at the Democracy Monument -- a stone's throw from the city's famed backpacker zone -- followed by a burst of gunshots, police said.

Bangkok's Erawan Emergency Centre said three people were killed and 23 wounded.

Hours later opposition demonstrators stormed a meeting between the government and vote officials, forcing caretaker Prime Minister Niwattumrong Boonsongpaisan and other ministers to flee.

"The election on July 20 is no longer possible. It must be postponed," Election Commission secretary general Puchong Nutrawong told AFP after the talks ended in chaos.

He said early August was one option for the polls but "may be too soon".

"The election cannot be held if protesters do not agree," Puchong added.

The deaths take the toll from six months of protests aimed at toppling the government to 28, with hundreds of others wounded in gun and grenade attacks mostly targeting opposition protesters.

There were no immediate reports of the identity of the gunmen behind Thursday's bloodshed, but both pro- and anti-government supporters are known to have armed hardliners and have blamed each other for previous violence.

Opposition shuns election

Fears have intensified that the nation's political deadlock could spiral into street clashes between rival protesters following the ousting of Yingluck by the Constitutional Court for the unlawful transfer of a top security official.

Her Red Shirt supporters have been holding a rally in a Bangkok suburb and have vowed to defend the government, which has limped on despite her removal from office, along with nine cabinet members.

An election held in February was later annulled after demonstrators blocked voting in many areas.

Anti-government protesters refuse to back new polls without poorly defined reforms first, saying the ruling Puea Thai party administration lacks the legitimacy to govern.

They are calling on the upper house of parliament, the Senate, to invoke a clause in the kingdom's constitution to remove the government and appoint a new premier.

But their critics say such a move has no legal basis.

Anti-government protesters have recently moved to the area immediately around Government House in the city's historic quarter -- a short walk from the site of Thursday's attack.

They are protected by several layers of concrete barriers and sand bags, while scores of protest guards patrol the area.

Protest leaders now occupy a wing of the government headquarters, holding press conferences in an attempt to show the government lacks the authority to rule.

Thailand has been cleaved apart by political divisions since 2006 when Yingluck's older brother Thaksin Shinawatra was ousted in a military coup.

Thaksin, a billionaire former telecoms tycoon, is reviled by the Bangkok elite and many southerners who accuse him of driving rampant corruption, cronyism and of being a threat to the revered monarchy.

But he has traditionally drawn strong support among the northern rural poor, who say he is the first Thai leader to improve their situation with populist policies and increasing political power.

Thaksin-led or aligned parties have won every election since 2001, but have also seen four premiers removed by coups or court rulings.