The US says the replacement of martial law with new emergency measures in Thailand does little to restore democracy in the military-run country.
Thailand's army, which took power in a coup in May, declared martial law over on Wednesday after almost a year.
But a section of the new constitution has been invoked instead under which the military retains significant power.
Critics have said Article 44 could lead to more draconian leadership and gives PM Prayuth Chan-Ocha unchecked power.
Security forces are still able to make arrests without warrants and detain people without charge, while Gen Prayuth - who led last year's coup - can rule by executive order in the name of national security.
The media remains heavily restricted and political gatherings of more than five people are still banned.
The US said it had wanted to see an end to detentions and the limits on freedom of expression.
"We are concerned that moving to a security order under Article 44 will not accomplish any of these objectives," a State Department official said.
"We would welcome the actual, full restoration of civil liberties in Thailand."
The move was also criticised as inadequate within Thailand.
Thitinan Pongsudhirak, a political scientist and director of the Institute of Security and International Studies at Bangkok's Chulalongkorn University, told reporters Thailand was "functionally in the same boat".
"Similar restrictions are still in place. And where there are pockets of dissent and political expression it is likely to be more draconian."
The Thai military government - officially known as the National Council for Peace and Order - has promised to restore democracy and hold elections in late 2015, but there is concern it is consolidating its power before then.
Officials had said the civil restrictions were necessary to maintain stability after the political unrest that preceded the coup. But the government had come under increasing pressure both from rights groups and from the vital tourism sector to end martial law.
On Wednesday, Gen Prayuth insisted Article 44 would be "exercised constructively", telling Thais: "Don't worry, if you're not doing anything wrong, there's no need to be afraid."
- September 2006: Army ousts Thaksin Shinawatra
- December 2007: Pro-Thaksin party wins election
- August 2008: Mr Thaksin flees Thailand
- December 2008: Huge anti-Thaksin protests; court bans ruling party; Democrat's Abhisit Vejjajiva comes to power
- March-May 2010: Huge pro-Thaksin protests; dozens killed in army crackdown
- July 2011: Yingluck Shinawatra, sister of Mr Thaksin, elected PM
- November 2013: Anti-government protests begin
- May 2014: Ms Yingluck removed from office; military launches coup
- August 2014: Coup leader Prayuth Chan-ocha named PM by legislature hand-picked by military