Thailand's ruling junta has warned protesters that it will not tolerate any further rallies against its coup after tense standoffs between soldiers and angry crowds in the capital Bangkok.

The army said demonstrators would be held for one or two days, but could be jailed for up to two years if they kept taking to the streets.

"We will give them a last chance today, but if they continue to rally, we will use measures to deal with them," said Lieutenant General Apirat Kongsompong, the AFP news agency reported.

On Sunday dozens of demonstrators faced off against lines of armed soldiers before and after more than 1,000 protesters marched through the city, the largest show of dissent since the army seized power on Thursday following months of political turmoil.

Hundreds of soldiers, most with riot shields, lined up to contain the crowd and there was some shouting and pushing and at least two people were detained, a Reuters reporter said.

Al Jazeera's Robert Kennedy, reporting from Bangkok, said several hundred protesters gathered in front of a McDonald's fast-food restaurant in the city's central business district, where soldiers with riot shields met them.

Chants of "Aok bai!" (Go away) rang out loudly through the cheering and jeering crowd, as soldiers sternly looked on.

Pushing and shoving broke out but there was no serious violence, Kennedy said.

"I think this coup is so bad," said a woman who asked to be identified only as Urai to protect herself. "The government was good and Red Shirts are good. These soldiers are bad."

Politicians detained

The military has detained former premier Yingluck Shinawatra along with scores of ousted government leaders, political figures, critics and academics in a sweeping roundup since the coup, which has drawn sharp international criticism.

The military has thrown out the constitution, censored the media and dismissed the upper house Senate, Thailand's last functioning legislature.

Power now lies in the hands of army chief General Prayuth Chan-ocha and his junta known as the National Council for Peace and Order, and their priorities appeared to be stamping out dissent and tending to the economy.

Critics say the coup will not end the conflict between the rival power networks: the Bangkok-based elite dominated by the military, old money families and the bureaucracy, and an upstart clique led by Yingluck's brother and former telecommunication mogul Thaksin Shinawatra.