BANGKOK (Reuters) - Thailand's government has vowed to go after shadowy "terrorists" it blames for triggering bloody clashes between the army and red-shirted demonstrators that left 25 people dead and more than 800 wounded on April 10.
It believes several hundred militants trained in combat are among protesters in their sprawling encampment in downtown Bangkok, well-armed and ready to attack security forces if they try to disperse the crowd.
Here are a few questions and answers about the mysterious black-clad fighters.
Witnesses and grainy video footage revealed armed men with assault rifles and M-79 grenade launchers appeared under cover of darkness on April 10 during a heated standoff between red shirts and troops trying to break up a protest in Bangkok's old quarter.
The government says the rebels, who wore black and covered their faces with hoods and balaclavas, appeared in the crowds of protesters and opened fire on troops, triggering chaos and prompting panicked soldiers to fire back in self-defense.
Government officials and the army believe the men in black are politically aligned with the red shirt movement and sought to cause bloodshed severe enough to force Prime Minister Abhisit Vejjajiva to call a new election.
Red shirt leaders say the "black clads" are protecting them, but they don't know who they are.
The government fears "terrorists" could strike at any time and may have been behind dozens of unsolved grenade attacks and bombings across the city, including those in the Silom business district on April 22 that killed one civilian and wounded 88.
Their presence among the protesters, and fears they have stashed away hundreds of assault rifles, M-79s, rocket-propelled or hand grenades, means any attempt to disperse the rally could be catastrophic, with massive casualties on both sides.
There are concerns that politically aligned armed groups could take part in militant activities if the stalemate persists. Attacks on troops or rival protesters could ensue, leaving Bangkok in a constant state of fear.
That's the big question no one has answered definitively. Whoever they are, the military is clearly alarmed. The army chief, Anupong Paochinda, admitted for the first time on Sunday that former or serving military personnel may be among them.
Military officials have said the men in black appeared well-trained in armed combat. The killing of a top commander, a former bodyguard of Queen Sirikit, was widely seen as an assassination.
Some security and military analysts believe rangers trained in counter-insurgency may be among them. These units fought communist rebels in the late 1970s.
A number of their units were disbanded or restructured in 2000, meaning plenty of ex-rangers are around who could have provided training for red shirt security personnel -- estimated by the government to be around 1,000 -- or may have even taken up arms themselves. WHO IS LEADING THEM?
Very difficult to know for sure.
Former army chief and prime minister Chavalit Yongchaiyudh, a close political aide of ousted prime minister Thaksin Shinawatra, the de facto red shirt leader, is credited with setting up the rangers. Abhisit suggested on Sunday that Chavalit, the chairman of the pro-Thaksin opposition party, Puea Thai, was involved at some level. Chavalit has denied that.
Others under suspicion by the government and military are retired generals who were purged when Thaksin was toppled in a military coup in 2006. The government has made no arrests, nor cited any evidence of their involvement.
Pallop Pinmanee, a hawkish Vietnam War veteran, is another name suggested. He is a retired four-star general, Puea Thai Party member and close associate of Chavalit.
Another is Khattiya Sawasdipol, a rogue major general known as "Seh Daeng," a major supporter of the red shirts who enjoys celebrity status. He is currently suspended after visiting Thaksin in Dubai without authorisation.
Both said in February that they wanted to set up a "people's army" -- comments Chavalit and the red shirts quickly distanced themselves from. Pallop and Khattiya have denied involvement in any of the violent incidents.
Editing by Bill Tarrant