MANDALAY, Myanmar — A provincial court in Myanmar on Thursday sentenced the head of a weekly newspaper and four of its journalists to 10 years in prison and hard labor for publishing a report that said a vast and secretive government factory was designed to produce chemical weapons.

Burmese journalists said the jail terms were a major blow to recently won news media freedoms in the country after five decades of censorship and persecution.

The five people sentenced Thursday in Pakokku Township Court included four reporters and the chief executive of the Unity journal, which closed in June partly because of the expense related to the case.

“This is injustice!” U Tint Hsan, the chief executive of Unity, shouted to reporters as he was led away from the courtroom. “This is an attempt to control the press!”