Thai anti-coup protesters squared off against soldiers in Bangkok Sunday in a growing show of dissent despite warnings from the ruling junta to end rallies, after the army consolidated all law-making authority.

The military has detained former premier Yingluck Shinawatra and scores of other ousted government leaders and political figures following a coup that has provoked sharp international criticism.

Dozens of protesters with large banners that read "Junta Out" and "Stop Coup" staged a boisterous demonstration, jeering angrily and pushing at lines of armed soldiers outside a shopping mall in the heart of Bangkok's retail district.

At least two protesters were taken away by the troops, according to AFP journalists at the scene.

One man was dragged away bleeding, while other demonstrators spat at soldiers as pockets of defiance against the army's takeover continued to multiply.

The protest came after the junta issued a fresh warning on Sunday against the use of social media to "incite" unrest.

"I ask for people's understanding on the current situation and that they refrain from anti-coup rallies, because democracy cannot proceed normally at the moment," said army spokesman Colonel Winthai Suvaree.

He said those detained by the military were being held without restraints and had not been "tortured or beaten" and reiterated that they would be released within seven days.

Those being held include politicians and leaders from both sides of the country's warring protest movements, while the army has summoned academics and journalists seen as critical to the coup.

Thailand has been rocked by persistent and sometimes violent political turmoil for nearly a decade, with bitter divisions intensifying in the years following the 2006 ouster of Yingluck's brother Thaksin by royalist generals.

Thaksin and his allies have won every election in Thailand this century, helped by the polling might of his support base among the working class and communities in the north and northeast.

But he is reviled by parts of the elite, the Bangkok middle class and southerners -- an alliance with wide influence in the establishment and army but little electoral success.

Growing concerns

Bangkok has seen several outbreaks of protests against the junta since army chief General Prayut Chan-O-Cha launched a dramatic takeover on Thursday.

Witnesses also reported protests overnight in parts of Thaksin's northern heartlands, with rallies in the city of Khon Kaen and a heavy military presence in Thailand's second largest metropolitan hub Chiang Mai.

The military junta on Saturday announced it had disbanded the Senate and placed all law-making authority in Prayut's hands.

Civil liberties have been curbed, media restrictions imposed and most of the constitution abrogated.

Thai journalist Pravit Rojanaphruk was the first reporter summoned by the junta. He reported to a Bangkok army conference centre on Sunday with black tape across his mouth in protest, according to witnesses.

Analysts have said the developments were an ominous signal that the army is digging its heals in and may be unwilling to relinquish power to a civilian government in the near term.

Washington, long a key ally, has led international condemnation of the coup.

It has suspended $3.5 million in military assistance, cancelled official visits and army exercises and said its remaining Thai aid budget was under question.

"We are increasingly concerned about actions the military has taken, just a few days after it staged a coup," State Department spokeswoman Marie Harf said in a statement Saturday, pointing to the dissolution of the Senate, arrests and media restrictions.

"We again call on the military to release those detained for political reasons, end restrictions on the media and move to restore civilian rule and democracy through elections."

The military said Saturday that Prayut had sent a letter regarding his takeover to the country's revered king, Bhumibol Adulyadej.

The monarch, 86, commands great respect among his subjects, and his blessing is traditionally sought to legitimise Thailand's recurring military takeovers.

The army said the king had "acknowledged" Prayut's letter, but stopped short of describing the response as an endorsement.

Thailand's powerful military has repeatedly intervened in politics, with democratic rule assaulted by 19 actual or attempted coups since 1932.