Thailand's army chief has warned that he will use force against demonstrators if anti-coup protests flare up again.

The threat is directed against protesters who have pledged to rally in Bangkok on Monday for a fourth day of demonstrations against the military's seizure of power. 

General Prayuth Chan-ocha who was recently given a royal endorsement to govern the country, said those found violating martial law could be tried in military courts, in his first press conference as de facto Thai leader.

If rallies continue "I will intensify law enforcement", he warned, adding "when the situation relaxes we can relax those measures".

Asked how long the military government would be in power he said the army would take control "until the situation is resolved" refusing to be drawn on whether he would eventually become prime minister.

In an effort to curb protests coup-maker Prayuth has ushered in orders curbing media freedoms and banning political gatherings of more than five people.

Meanwhile, anti-coup protesters have held several seemingly spontaneous rallies in downtown Bangkok since last Friday.

On Monday, about 100 people gathered at Bangkok's Victory Monument where about 1,000 protesters massed on Sunday.

Demonstrators, many holding anti-coup placards, scuffled with soldiers and several have been detained, raising fears of a wider crackdown if they continue to breach martial law.

Prayuth seized power on May 22, saying the army would restore order after nearly seven months of sometimes deadly street demonstrations against the government of Prime Minister Yingluck Shinawatra.

Yingluck herself was detained by the military on Friday, but it has relaxed restrictions, allowing her to go home although she is under military supervision, Reuters reported.

The military took over the government with a heavy hand: detaining scores of people, most allied with Yingluck's government, throwing out the constitution, dissolving the Senate and censoring media, Reuters news agency reported.

The military has also ordered dozens of outspoken activists, academics and journalists to report to military authorities. More than 200 have been officially summoned so far in lists broadcast on radio and TV.

Source: Agencies