The State Department's top human rights official is accusing Myanmar authorities of resorting to police-state tactics after five journalists from a weekly magazine got 10 years at hard labor for a disputed story about a weapons factory.

Assistant Secretary of State Tom Malinowski's comments, in an Associated Press interview Wednesday, are the stiffest U.S. criticism yet following last week's sentences. The case is troubling for the Obama administration, which has cast its support of Myanmar's democratic reforms as one of its important foreign policy achievements.

Malinowski said the U.S. remained committed to engagement with Myanmar's government as it grapples with difficult institutional reforms and shifts the nation also known as Burma from five decades of direct military rule. He urged protection of the press freedoms that were unleashed when a repressive junta ceded power three years ago. He said that would be crucial to its democratic transition and for the credibility of national elections next year.

The chief executive and four reporters of the journal Unity were charged under a colonial-era security law. Myanmar authorities have defended the arrests as a matter of national security. The magazine has since gone out of business.

The punishment has raised alarm among rights groups and Myanmar journalists. Police have also opened a case against 50 journalists after they staged a peaceful protest in the main city of Yangon against the sentences. They could face charges for violating a law on peaceful assembly that carries a six-month prison term.

"The release of political prisoners has been one of the most important success stories of the last couple of years, and it would be unfortunate if we got back to having to address more cases like that," Malinowski said.

"So obviously sentencing a journalist to 10 years' hard labor for reporting the news, whatever one thinks of the quality or accuracy of a particular news story, is not a great sign," he said.

Malinowski urged that the case be reviewed and that any journalists prosecuted for reporting a story be freed.

Malinowski, who raised the issue of press freedoms when he met top government and military officials in Myanmar in late June, said concerns over journalistic ethics and irresponsible reporting were legitimate and to be expected in Myanmar's fledgling media but the U.S. has stressed "the way to deal with those problems is not through the tactics of a police state."

"If your response is to arrest journalists, we are going to go back to the kind of relationship between Burma and the rest of the world that is not in your interests," he said.

Unity had reported in late January that the military had seized farmland and constructed a chemical weapons factory in central Magwe Region. It printed a denial from authorities.

Government spokesman Ye Htut did not respond to an email requesting comment Wednesday. After the arrests of the journalists in February, he told The Irrawaddy, a Thailand-based online news site, that it was a national security issue and even a country like the U.S. would respond in the same way.

Zaw Thet Htwe, a journalist and member of the Myanmar Press Council, likened it to treatment of journalists under the former ruling junta and said it did not augur well for democratic reforms.

Zaw Thet Htwe is one at least 14 journalists among the more than 1,100 political prisoners who have been freed by President Thein Sein's quasi-civilian administration. He had been sentenced to death by a military court in 2003 for publishing articles critical of the military; his sentence was commuted.

David Mathieson, senior researcher on Myanmar for Human Rights Watch, said new laws this year have also stifled press freedom, and there have been cases of journalists held on spurious charges.

Last week, five staffers of the Bi Mon Te Nay weekly were arrested and are being charged under a security law for publishing an article suggesting opposition leader Aung San Suu Kyi would be installed as leader of an interim government.

Outbreaks of deadly anti-Muslim violence and the uncertain prospects for reforming the current military-dominated constitution have also raised questions from U.S. lawmakers about whether the Obama administration moved too quickly in easing sanctions against Myanmar and ramping up aid.

Malinowski said he did not believe Myanmar was backtracking on reforms but was now in a more difficult stage in its transition that requires fundamental legal and institutional changes. Despite new openness, many laws on its books date back to a more repressive era, leaving journalists and civil society activists still vulnerable to prosecution, he said.

"I see a contest between people who are trying to push this remarkable transformation forward and those who are either confused or threatened by the rapid pace of change," he said.

Malinowski said the U.S. would encourage Myanmar to keep up the momentum on reforms ahead of the 2015 national elections, a key test of its democratic progress.