Plumes of smoke could be seen over a tense Bangkok early Saturday as the death toll from the latest clashes between the Thai army and anti-government "Red Shirt" protesters hit 16.
 

A Thai soldier sets a razor wire cordon after clashes with anti-government protesters in Bangkok. (AFP/Pornchai Kittiwongsakul)

Violence continued overnight after troops on Friday opened fire on demonstrators during a military lockdown of their vast fortified rally site in the heart of Bangkok.

Soldiers have blocked roads and set up checkpoints to seal off the area around the wider protest site, which extends for several square kilometres (miles).

The protesters, who are trying to bring down the government of Prime Minister Abhisit Vejjajiva, threw stones, used slingshots and launched fireworks at the troops as the two-month standoff descended into more violence.

A total of 16 people -- all of them Thais -- were known to have died since the fresh wave of violence began, according to the official Erawan emergency centre.

The centre said 141 people had been injured, three of them foreigners, whom it identified as being from Canada, Myanmar and Poland. No details were given of their condition.

The France 24 television station said one of its journalists -- a Canadian -- had been shot and wounded covering the arrest, while two Thai reporters were also amongst the injured. A Japanese cameraman was killed here last month.

Government spokesman Panitan Wattanayagorn said troops had come under attack as they moved to seal off the rally area to prevent more Red Shirts from entering.

"The soldiers... had no choice but to respond to these attacks," Panitan told reporters Friday. Troops were authorised to use live ammunition in self-defence, for warning shots or against armed gunmen, he added.

Troops would step up security measures in the coming days to search for weapons and reduce the number of people entering the area, he said, warning of the risk of more instability in the capital.

The United States called for restraint on all sides.

"We are deeply concerned about the situation on the ground in Thailand," State Department spokesman Philip Crowley told reporters.

"We continue to strongly encourage everyone involved... to show restraint and to find a way to work peacefully through these differences and do so in a way that strengthens democratic institutions," Crowley added.

UN Secretary General Ban Ki-moon said he was following the rapidly mounting violence and tensions in Thailand with "growing concern".

"He appeals to both the protesters and the Thai authorities to do all in their power to avoid further violence and loss of life," Ban's press service said in a statement.

"He strongly encourages them to urgently return to dialogue in order to de-escalate the situation and resolve matters peacefully," it said.

The violence came after Abhisit shelved a plan to hold early elections in November after reconciliation efforts broke down.

The mostly poor and working class Reds consider Abhisit's government illegitimte because it came to power in a 2008 parliamentary vote after a court ruling ousted elected allies of their hero, former premier Thaksin Shinawatra.