Send good karma, post a photo, criticize the prime minister - all things you can do with the click of a mouse at Facebook.

But in Croatia, the last one might be a click too far. A man who launched a Facebook group critical of Prime Minister Ivo Sanader has been detained and questioned by police.

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Some in the country are crying foul, sensing a move to quash cyber-debate.

Political analyst Jelena Lovric called the detention a "notorious abuse of police for political purposes." And the leader of the opposition Social Democrats, Zoran Milanovic, said the police action endangered freedom of expression.

The kerfuffle in the Balkan country had its origins several months ago when Niksa Klecak, 22, set up an anti-Sanader group on Facebook, the social networking website. The name of the group was, "I bet I can find 5,000 people who dislike Sanader."

Last week, though, the hammer fell. Police questioned Klecak for three hours and searched his home and computer.

Krunoslav Borovec, a senior national police official, rejected criticism of the detention. Police acted legally, he said, because Klecak's group displayed a photo montage of Sanader in a Nazi uniform. Nazi symbols are banned under Croatian law.

Croatian police chief, Vladimir Faber, also insisted the investigation was "motivated by the content, not the author's political affiliation."

And the prime minister himself had no problem with the police action, either.

"There is no satire with Nazi insignia," Sanader told Croatian state-run radio. "The photo montage, he said, "was not an attack on me, but Croatian democracy."

But Klecak, who is a member of the Social Democrats' youth branch, wasn't buying the explanation about Nazism. He was convinced, he said, that his was a "politically motivated case."

Lovric, the political analyst, said the case exposed officials' fear of the web. The government "cannot influence internet, and that deeply frightens it," Lovric said.

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Traditional Croatian news organisations are relatively free, although they do face pressure from political or business interests. But opposition against Sanader is boiling on websites - and it has exploded since the police action against Klecak.

The government may find quashing debate on the web a bit difficult. New anti-government Facebook sites are popping up like animals in the Whack-A-Mole arcade game.

One, calling for a protest against Sanader later this month, has gathered 80,000 members. Klecak's group has grown to 6,200 members since Friday - exceeding his original goal of 5,000. And another Facebook group, called "Search my flat, you Gestapo gang, Croatia is not a police state," surfaced over the weekend and already has about 2,600 members.

By contrast, a group called "I bet I can find 7,000 people who LIKE Sanader" has just 19 members so far.

Still, the online activists may find that cyber-protests don't necessarily translate into real ones. It's easier to click a mouse than to take to the streets. A Facebook-launched protest against mafia-style murders in Zagreb, the capital, drew just a few hundred people.

And in Egypt earlier this year, a Facebook group called for a general strike on President Hosni Mubarak's 80th birthday. The group had 60,000 cyber-members, but the protest was a bust.

And real-life detention and questioning can certainly make a point. Damir Kajin, another opposition politician in Croatia, said the police action "was a message to those who found a new way of political fighting on the internet."