Bangkok - The deaths of four Thai children from attacks on anti-government protest sites over the weekend sparked calls on Monday for a peaceful solution to the country's political deadlock.

One 5-year-old boy and three girls aged 5 to 6 fell victim to violent attacks over the weekend, one in Bangkok and the other in the eastern province of Trat, 250 kilometres south-east of the capital.

On Saturday night, unknown assailants lobbed grenades and fired automatic rifles into an anti-government demonstration in Khao Saming district of Trat, killing a 5-year old girl and wounding more than 30 people, police said.

A grenade exploded Sunday at a protest site in central Bangkok killing a 40-year-old woman and five-year-old boy on the spot.

Two young girls died in hospital on Monday from their injuries.

A police officer who had sustained a head wound during a crackdown on a protest site on February 18 also succumbed to his injuries in hospital on Monday, bringing the total death toll from political violence over the past week to 11.

Four protesters died in the February 18 crackdown.

The central intersection where Sunday's explosion occurred is one of five sites still occupied by protesters in their months-long bid to force caretaker Prime Minister Yingluck Shinawatra and her cabinet to resign.

United Nations Secretary General Ban Ki-moon on Sunday condemned the spike in Thailand's political violence.

Ban urged “the parties to respect human rights and the rule of law, prevent any new attacks and engage in meaningful dialogue toward ending the crisis and advancing reform,” he said.

The protesters and the government have blamed each other for harbouring “hidden forces” to carry out the violent acts.

The military, which has staged 18 coups over the past eight decades, has so far played a neutral role in the political conflict.

Army Commander-in-Chief General Prayuth Chan-ocha on Monday urged a peaceful solution to the conflict, in accordance with law.

“There are many sides that want the army to come out, but if we come out it will not solve the problems because there would be fighting and the country might collapse,” Prayuth said.

Protest spokesman Akanat Promphan demanded the government accept responsibility for the mounting violence, noting that it had failed to hold anyone accountable for clashes and attacks that have left at least 21 dead and 719 injured since the protests began, according to government figures.

Paradorn Pattanatabut, secretary general of the National Security Council, blamed opposition “extremists” for the weekend violence.

“I can assure you that the government and pro-government groups were not involved in the violent incidents,” Paradorn was quoted by the government-run MCOT news service as saying.

Regular protests centred in Bangkok have been going on since early November, demanding the premier's resignation to pave the way for an appointed government and political reforms.

Sapa-dpa