"They took this action unilaterally. The government is having a special meeting regarding this. We have to watch and see if the army chief honors his declaration of impartiality," the aide said, describing the situation as "half a coup d'etat."

Lt. Gen. Nipat Thonglek told CNN the move was not a coup.

"The Army aims to maintain peace, order and public safety for all groups and all parties," a ticker running on the army's television channel said. "People are urged not to panic, and can carry on their business as usual. Declaring martial law is not a coup d'etat."

Martial law went into effect at 3 a.m. on Tuesday, the ticker said.

All Thai TV stations are being guarded by the military, Thai public television announced, showing pictures of soldiers and armored vehicles taking positions outside broadcast facilities in the country's capital.

In a statement read on Thai television, the military declared that all of the country's radio and television stations must suspend their normal programs "when it is needed."

The dramatic announcements come days after the head of the army issued a stern warning after political violence had surged in the country's capital.

Political tensions have been running high in Thailand. Supporters and opponents of the country's government have staged mass protests in recent days, and caretaker Prime Minister Yingluck Shinawatra was removed from office, along with nine cabinet ministers, by a top court earlier this month.

Thitinan Pongsudhirak, a political science professor, described the situation as "very volatile."

"This is a precarious time now for the army," he said. "They have to be even-handed."

If the military appears to be favoring one side, he said, violence could escalate rather than cool down.

"If it's seen as favoring one side or the other side, then we could see more violence and turmoil against the military," he said.

Nipat said the precise restrictions of martial law were being worked out.

The government's "red shirt" support base, many of whom hail from the country's rural north and northeast, view Yingluck's ouster as a "judicial coup" and have been protesting what they consider an unfair bias by many of the country's institutions against their side.

Anti-government protesters are seeking a new government -- but not through elections, which the opposition Democrat Party has boycotted, arguing the alleged corruption of their political rivals makes widespread reform necessary before any meaningful vote can be held.

Source:CNN News International