Washington has accused the military-backed government in Burma of threatening pro-democracy leader Aung San Suu Kyi and her party.
US state department spokesman PJ Crowley said the government's attitude showed things had not changed despite last year's election.
"Burma claims there is a new era, but it is up to its old tricks," he said.
On Sunday Burmese state media warned Ms Suu Kyi and her party could meet a "tragic end" because of their policies.
The commentary was the first direct criticism of Ms Suu Kyi since her release from house arrest.
She and her party, the National League for Democracy (NLD), were criticised for continuing to endorse Western sanctions.
The NLD said recently it did not see any reason for lifting international sanctions on Burma now.
Mr Crowley released his reaction on microblogging website Twitter.
"Burma claims there is a new era, but it is up to its old tricks by threatening Aung San Suu Kyi," he tweeted.
"New suits does not a new system make."
The NLD were excluded from last year's election, the first in 20 years.
Burma's veteran military leader, Gen Than Shwe, proposed the members of the new government and the army still dominates parliament.
Ms Suu Kyi and her party won Burma's 1991 election overwhelmingly only to see it nullified by the military.