Caretaker Prime Minister Yingluck Shinawatra has asked the military to help police enforce law and order if protest leader Suthep Thaugsuban carries out his threat to "shut down" Bangkok.
A Defence Ministry source said the prime minister is worried by the People's Democratic Reform Committee (PDRC)'s threat and wants the military to intervene.
"It seems the country is in a state of lawlessness. People can do what they want," the source quoted Ms Yingluck as telling the armed forces leaders at a meeting on Wednesday.
She also asked the army chief to hold talks with Mr Suthep or to help broker another meeting between her and the protest leader, the source added.
Army Commander Gen Prayuth Chan-ocha appeared uneasy about using soldiers to help police, the source said. The army was heavily criticised over its role in the 2010 political violence.
"What can the military do? We can't disperse the protesters like we did in 2010. Soldiers became the bad guys and ended up being charged," he was quoted as saying.
The source said Ms Yingluck also asked military leaders if they would be interested in joining a proposed political reform assembly.
PDRC spokesman, Akanat Promphan, yesterday denied a rumour the Bangkok shutdown includes a plan to cripple public transport with BTS, bus and airport seizures.
He said locking down Bangkok will send the message to Ms Yingluck that Thais want to see peaceful national reform, which could be achieved if she resigned.
"If this move fails, more aggressive action would be implemented, based on our non-violence principle," he said.
He also said the PDRC would not hold talks with the Election Commission.
Meanwhile, a special unit will be deployed to protect crowd-control police if violence flares with protesters, said national police chief Adul Saengsingkaew.
If there is use of weapons, the unit will protect the lives of officers, he said.