YANGON -- Two Myanmar journalists working for a weekly newspaper have been arrested, but police gave no reason for their detention, an editor at the paper said Tuesday.

Editor-in-chief Thet Zin and managing editor Sein Win Maung were arrested on Friday night and remain under investigation, another editor at the weekly Myanmar Nation told Agence France-Presse, speaking on condition of anonymity because he feared to talk openly about the arrests.

"We don't know the reason why they were taken for questioning," he said.

"Other than their arrests, the paper is still operating. The paper is not involved in anything and other editors are working normally. We have been running the journal since 1989," he said.

The mystery surrounding their arrests prompted speculation that they may have secret links with the pro-democracy opposition or with exiled dissidents in Thailand.

The editor insisted that police had not confiscated anything from the paper's offices, but others said that authorities had seized documents and videos related to mass anti-government protests in September.

Police have clamped down on anyone suspected of sending images and news about the protests to foreign news media.

All media in Myanmar are tightly controlled by the government, but ordinary citizens and Internet users sent a flood of pictures and information about the protests to media around the world.

At their peak, more than 100,000 people took to the streets of Yangon and other cities, in demos led by Buddhist monks in the biggest challenge to military rule in nearly 20 years.

Some journalists were briefly detained during the protests and the deadly crackdown that followed, when the UN estimates at least 31 people were killed.