MINSK (Reuters) - Three journalists working for independent news outlets in Belarus were detained on Tuesday on suspicion of hacking the computer systems of state-run news agency BelTA and stealing its data, the authorities said.

The Belarusian Association of Journalists and local media said five people had been detained for a period of three days and several more detained for questioning. Reuters could not independently confirm that information.

Investigators said they had opened a criminal case against two editors from the privately-owned independent news website “Tut.by”, the biggest online news portal in the country with 800,000 daily unique users, and against one journalist from the independent news agency BelaPAN.

Local rights groups said the arrests were part of a government drive to muzzle independent media. Last year, the Belarusian authorities put down peaceful opposition protests in a severe crackdown which ended a brief period during which the government had eased its authoritarian rule.

“Without the knowledge or agreement of the republican unitary enterprise (BelTA), information held on its computer system was accessed illegally more than 15,000 times over a two-year period,” investigators said in a statement.

Nasha niva, another independent news website, cited a representative of BelTA as saying the detained journalists had used other people’s passwords to access its news wire.

Yuri Zisser, the owner of Tut.by, told Reuters that BelTA had never complained before about the use of its information.

“I’m really confused and don’t understand what this is about and why it’s needed,” he said.

Ales Lipai, the director of BelaPAN, said the case was a mystery that had come out of the blue.

“All of BelTA’s material is freely available. It’s written on their website that you can use their material as long as you provide attribution, which is what we did.”

A spokesman for the Council of Europe’s secretary general called on the Belarusian authorities to free the detained journalists and conduct a transparent investigation.

A spokesman for the Belarusian Foreign Ministry said the detentions had nothing to do with freedom of speech.

“This is purely a legal matter,” the ministry said in a statement.

Andrei Bastunets, head of the Belarusian Association of Journalists, said government pressure on independent media had been on the rise in the last year.

“I link this (case) with the general trend and the desire to control the internet space,” he said of the detentions.

President Alexander Lukashenko has run Belarus along Soviet-style command lines since 1994. He has heeded some calls from the West to show more leniency toward political opposition, but opponents say their freedom to operate remains severely limited.