Thailand's new leaders have banned all meetings and other activities by political parties, two days after taking power in a military coup.
They also say they have assumed legislative powers and duties in the absence of a parliament.
Two of ousted PM Thaksin Shinawatra's ministers were detained by the military leaders, joining his deputy PM and top aide who were already being held.
Mr Thaksin said he planned a "deserved rest", but called for quick elections.
Coup leader Gen Sonthi Boonyaratglin has proposed a year-long transitional period as a constitution is drafted.
But opposition leader Abhisit Vejjajiva challenged the military's timeframe and called for elections in six months.
US Assistant Secretary of State Chris Hill said the country was reviewing its aid to Thailand, and described the coup as a "very sad development" for Thai democracy.
Bangkok residents returned to work on Thursday for the first time since Tuesday's bloodless takeover, with tanks continuing to patrol the capital's streets.
The ruling council, headed by coup leader Gen Sonthi, declared a ban non political activities - including the formation of new parties - and replaced four of Mr Thaksin's top security officials.
It also summoned the editors of a number of television stations and asked them not to broadcast opinions from the public sent in by text message.
The military has been blocking broadcasts it deems harmful, and had already forbidden gatherings of more than five people.
A statement said the restrictions on political activity would be reversed when normality returned.
The BBC's Jonathan Head in Bangkok says opinion polls suggest most Thais - both urban and rural - have accepted the military takeover as a necessary step to end the crisis over Mr Thaksin's leadership.
But, he says, they may be less willing to accept the military leaders' mounting restrictions.
Call for elections
But Mr Thaksin, speaking from London where his is on a private visit, called for national reconciliation.
"We hope the new regime will quickly arrange a new general election and continue to uphold the principles of democracy for the future of all Thais," a statement said.
Mr Abhisit, who leads the Democrat party, the main opposition to Mr Thaksin, said he was not overly alarmed by the coup leaders' new measures but wanted clarification.
He earlier denied that a new constitution was needed, and said elections could be held in six months.
"The country has to move forward and the best way forward is for the coup leaders to quickly return power to the people and carry out reforms they promised," he said.
The coup followed months of growing tension in Thailand, with protests against Mr Thaksin and a general election which was annulled due to concerns about its legitimacy.
Gen Sonthi has said he was acting in line with the wishes of the Thai people, accusing Mr Thaksin's government of corruption and fostering divisions in the country.
The coup leader has promised to appoint a new prime minister within two weeks, and said the interim government would draft a new constitution with the aim of restoring democracy within a year.
Internationally, the coup has been widely condemned.
According to Thai state TV, Thailand's revered head of state, King Bhumibol Adulyadej, has given his backing to Gen Sonthi.
The general is believed to be close to the king, although he says the monarch had nothing to do with the actual coup.
Correspondents in Bangkok say securing the endorsement of the 78-year-old monarch is crucial to the success of the military intervention.