The Thai government appealed to the military Friday to provide security for February elections after violent clashes between police and opposition protesters left two people dead and more than 150 wounded.
With tensions running high in the capital, the army chief refused to rule out a coup, saying "anything can happen".
Prime Minister Yingluck Shinawatra's government has pledged to go ahead with the polls in the hope of calming weeks of mass street demonstrations seeking to curb her family's political dominance.
The protesters have vowed to block the vote, saying it will only return the Shinawatra clan to power.
A policeman and a civilian died of gunshots fired by unknown assailants while 153 people were injured after violence erupted Thursday when demonstrators tried to force their way into an election registration venue.
The security forces denied using live ammunition.
Deputy Prime Minister Surapong Tovichakchaikul said he would ask the armed forces supreme commander for help with security for a second round of registration for constituency candidates due to begin around the country on Saturday.
"I will also ask the military to provide security protection for members of the public on the February 2 election date," he said in a nationally televised address.
The army chief insisted Friday that the military would remain neutral and said it was up to the election authorities whether the vote could go ahead.
"Don't bring us into the middle of the conflict," General Prayut Chan-O-Cha said when asked if the army would send soldiers to guard polling stations.
But he did not rule out another coup.
"The door is neither closed nor open. In every situation, anything can happen," he said when asked about the possibility of a coup, without elaborating.
Yingluck's government -- which still enjoys strong support in the northern half of the country -- has faced weeks of mass street rallies in the capital.
Thailand has been periodically convulsed by political bloodshed since Yingluck's older brother Thaksin Shinawatra was overthrown by royalist generals in a coup seven years ago.
Thaksin's Red Shirt supporters -- who staged their own mass street protests against the previous government three years ago -- warned Friday that they were ready to return to the streets if elections were thwarted.
"After the New Year we are preparing for a major battle," core Red Shirt leader Jatuporn Prompan told reporters.
Supporters of Thaksin, a billionaire tycoon-turned-politician who lives in self-exile, have accused the demonstrators of trying to incite the military to seize power again, in a country which has seen 18 successful or attempted coups since 1932.
But so far the army -- traditionally a staunch supporter of the anti-Thaksin establishment -- has avoided any public intervention in the unrest, apart from sending a limited number of unarmed troops to guard government buildings.
The protesters, a mix of southerners, middle class and urban elite, accuse Thaksin of corruption and say he controls his sister's government from his base in Dubai.
They want an unelected "people's council" to run the country to oversee loosely-defined reforms -- such as an end to alleged "vote buying" -- before new elections are held in around a year to 18 months.
The weeks-long unrest, which has drawn tens of thousands of protesters onto the streets, has left seven people dead and about 400 wounded.
It is the worst civil strife since 2010, when more than 90 civilians were killed in a bloody military crackdown on pro-Thaksin Red Shirt protests under the previous government.