An explosion and gunfire rang out near a sprawling anti-government protest site in the Thai capital early on Tuesday after the protesters' leader warned that government supporters were planning to bring armed militants to Bangkok.
Weeks of unrest, in which protesters have barricaded key intersections of the city, have been interrupted by occasional bombs and gunfire, with one blast killing a woman and a young brother and sister in a central shopping district on Sunday.
There was another explosion and gunfire near one protest site on the edge of Bangkok's Lumpini Park in the early hours, national security chief Paradorn Pattanathabutr told Reuters.
Two men were wounded, medical sources said.
"Last night, we don't know where and who it came from, but there was an explosion and gunfire sound from 1 a.m.," Paradorn said. "Officials will investigate the area this morning and there should be more information soon."
He also said there was an explosion near the office of the opposition Democrat Party. No one was hurt.
The protesters, who disrupted a general election this month leaving the country in political limbo, aim to unseat caretaker Prime Minister Yingluck Shinawatra and erase the influence of her brother, former premier Thaksin Shinawatra, seen by many as the power behind the government.
Protest leader Suthep Thaugsuban accused Jatuporn Promphan, a leader of the "red shirt" supporters of Thaksin, of wanting to bring armed militants to Bangkok from their power base in the mainly rural north and northeast, setting the stage for potential conflict.
He also accused police of doing nothing about it.
"It is clear that Jatuporn wants to divide the country in two," he told supporters late on Monday.
Yingluck called for dialogue to resolve the crisis.
"It's time all sides turned to talk to each other," she told reporters on Monday. "Many people have asked me to resign but I ask: Is resignation the answer? What if it creates a power vacuum?"
In a measure of the economic impact of the crisis, flag carrier Thai Airways International releases its 2013 earnings on Tuesday. It is expected to report a huge loss and may cite a slump in tourism since late last year as a factor.
Trade figures for January could also show the biggest fall in imports since the global financial crisis as consumption, construction and other activities weaken.
At least 20 people have been killed and more than 700 wounded since the protests began in November.
They are the biggest since deadly political unrest in 2010, when Thaksin's red shirts paralysed Bangkok. More than 90 people were killed and 2,000 wounded during that unrest, which ended when Suthep, then a deputy premier, sent in troops.
Demonstrators accuse Thaksin of nepotism and corruption and say that, prior to being ousted by the army in 2006, he used taxpayers' money for populist subsidies and easy loans that bought him the loyalty of millions.
(Writing by Nick Macfie; Editing by Alan Raybould and Paul Tait)