A woman and a child were killed in a grenade attack Sunday in a main Bangkok shopping district, drawing the Thai prime minister's denunciation of "terrorist acts" as fears over violence mount after nearly four months of political crisis.

The Sunday afternoon attack came a day after a young girl died and dozens were hurt in a drive-by shooting at a protest rally in eastern Thailand.

The explosion occurred during an anti-government rally in an area popular with tourists for its street stalls, hotels and proximity to one of the biggest shopping malls in Thailand's capital.

"A 40-year-old woman and a 12-year-old boy died and 22 people were injured," the Erawan emergency centre said in an update on its website. Two children were among the injured.

A damaged tuk-tuk was left abandoned on the blood-splattered road as soldiers and police sealed off the area.

Police said shrapnel fragments indicated the blast was caused by a grenade fired from a M79 launcher.

In a posting on her official Facebook page Premier Yingluck Shinawatra denounced the incidents as "terrorist acts for political gain", stating the childrens' deaths "were particularly saddening and disturbing".

UN Secretary General Ban Ki-Moon also condemned the escalation of violence in Thailand over the past week, a spokesperson said, "in particular armed attacks against protesters in which even children have been killed".

He called for violence "from any quarter" to cease immediately.

Thailand has seen months of anti-government rallies aimed at ousting Yingluck's embattled administration.

The protests have been met with sporadic gun and grenade attacks -- mainly in Bangkok -- by unknown attackers.

On Saturday a five-year-old girl died and 30 were injured -- including another girl -- when gunmen sprayed bullets at a anti-government rally in the Khao Saming district of Trat province, 300 kilometres (185 miles) east of the capital.

The kingdom has been bitterly split since a military coup ousted Yingluck's brother Thaksin Shinawatra as prime minister in 2006.

The current unrest is the worst since Thaksin-allied Red Shirt protests against a Democrat-led government in 2010 sparked clashes and a bloody military crackdown that left more than 90 people dead.

In recent months 19 people have died and hundreds more have been injured, fuelling fears of a spiral of unrest.

- 'A real fight' -

Red Shirt leaders met Sunday in Nakhon Ratchasima, the gateway to the Shinawatra-supporting northeast, to discuss ways to bolster Yingluck's crisis-hit administration.

Prominent leader Nattawut Saikuar warned the group was now in a "real fight" but refused to elaborate on its plans.

"We will carry on fighting to the end," he said, amid fears any street action by the group could lead to clashes.

Some analysts say the seemingly intractable crisis could lead to protracted violence or a form of wider civil conflict.

The political divide broadly pits the Thaksin-supporting rural north and northeast against anti-government protesters -- who represent the Bangkok-centred establishment as well as many southerners.

The anti-government movement seized on Saturday's drive-by attack in Trat as an example of authorities failing to protect rally-goers.

"Weapons of war were used in an act of planned and organised terror," protest spokesman Akanat Promphan told AFP.

"This atrocity has worsened the severity of the violence against innocent protesters... it is a matter of national security," he told AFP.

Both sides have traded blame for sparking previous clashes, including a dramatic gunbattle between police and protesters in Bangkok's historic heart last week which left five people dead -- including a policeman -- and dozens wounded.

Anti-government protesters are carrying out a self-proclaimed "shutdown" of several key intersections across Bangkok -- including near the site of Sunday's blast.

But their numbers are dwindling from highs of tens of thousands in the past.

Yingluck's government last week suffered another blow when a court banned it from using force against peaceful demonstrators, severely crimping its powers to handle the protests and mounting violence.

In a two-pronged challenge, the embattled premier is facing both street pressure and a series of legal threats from Thailand's notoriously interventionist courts.

She faces charges of neglect of duty over a controversial rice subsidy scheme that could see her removed from office.

Protesters accuse Yingluck's billionaire family of using taxpayers' money to buy the loyalty of rural voters through populist policies such as the rice scheme.

They are demanding that she step down to make way for a temporary unelected council that would oversee loosely defined reforms to tackle corruption and alleged vote-buying.