BANGKOK (REUTERS) - Thai authorities detained 20 student activists protesting against military rule on Friday, a year after the army seized power from an elected government.

The military has quashed public demonstrations and any sign of resistance to the May 22, 2014, coup which it says it was forced to undertake to end violence between rival factions.

The military government has promised a general election next year though critics worry about constraints on politics under a new constitution that they say is undemocratic.

Activists staged small shows of defiance to mark the anniversary of the takeover. Soldiers detained seven students, some who held anti-coup signs, after they gathered in the north-eastern city of Khon Khaen.

"We invited them to talk but they would not back down so we are sending them to the police," said a soldier in the area who declined to be identified.

In Bangkok, police detained 13 members of the Young People for Social-Democracy student group who were protesting against the coup. The activists were later released, the group said on its Facebook page.

Thailand has been mired for a decade in rivalry between the Bangkok-based establishment and ousted premier Thasksin Shinawatra, a former telecommunications tycoon who broke the mould of politics with pro-poor policies that won him the support of the poor but the hostility of the elite.

The government ousted last year was led by Thaksin's sister, the country's first woman prime minister, Yingluck Shinawatra.

A year later, the captains of industry remain firmly behind the junta, despite a lacklustre economy and a delayed return to democracy.

Human Rights Watch on Friday said the junta had systematically repressed human rights by banning political activity, censoring the media and trying dissidents in military tribunals.