BANGKOK (AFP) - Thailand's caretaker Prime Minister Niwattumrong Boonsongpaisan on Tuesday urged the nation's army to act within the constitution, in an official statement giving his first reaction to the military's declaration of martial law.

"Any actions need to follow a peaceful path, without violence, discrimination and with equality based on the rule of law," the statement, attributed to the premier, said.

It added that the military "must proceed under the constitution".

The army did not consult the government before imposing martial law early on Tuesday, in a move the military said was "not a coup" but aimed to restore order amid fears of widespread political violence.

Mr Niwattumrong replaced premier Yingluck Shinawatra after she was ousted by a controversial court ruling on May 7.

His government, which holds a caretaker role, has staggered on as anti-government protesters have sought support from the Thai upper house to remove him and appoint a new premier.

Critics say the Thai Senate lacks authority to carry out such a move.

Mr Niwattumrong wants fresh elections to cut a path through this round of Thailand's political crisis which is stretching towards its seventh month.

Observers say the ruling Peau Thai party is likely to win any new polls.

Anti-government protesters are calling for ill-defined reforms before new elections to end the dominance of Ms Yingluck's billionaire brother Thaksin on Thai politics.