A group of young Iranians who appeared in an Iranian online version of Pharrell Williams's hit song Happy have been arrested, it has emerged.

Iran's state-run national TV on Tuesday broadcast a programme showing men and women, apparently Pharrell fans from Tehran, confessing on camera.

They were supposedly involved in a video clip based on Pharrell's song. The original has been viewed almost 250m times on YouTube and has inspired people from all over the world to make their own version of the video, which shows people dancing in the street to the song.

Human rights activists have repeatedly condemned what they see as the state TV's common fashion of airing confessions made under duress, usually misrepresented as interviews.

It was not clear if Pharrell's fans in jail in Iran had access to their lawyer before appearing on television. They have not yet been tried. In recent years, many activists and political prisoners have appeared on the Iranian national TV making confessions.

Tehran's police chief, Hossein Sajedinia, confirmed six people had been detained in connection with "an obnoxious" video released on social networking websites, according to the semi-official Isna news agency.

"We launched a police investigation in cooperation with the judicial authorities and identified and arrested the accused within six hours," he told Isna. Sajedinia said those arrested acknowledged what he described as a wrongdoing.

In the TV programme, the detainees who are talking with their back to camera, appeared to say they were duped and the video was not meant to be posted online.

"They had promised us not to publish the video," a young women said on the programme. Another detainee said they appeared on the video to practise acting. On TV, Sajedinia warned Iranian youth that the police was vigilant and prepared to tackle those acting against the social norms.

At least two other Iranian versions of Happy have also been posted online but the one featuring the arrestees, which has now been taken offline, was viewed by tens of thousands of people. It showed Pharrell's jubilant fans dancing and singing on the rooftops of Tehran with the city's iconic Milad tower in the background.

"Iran is a country where being "happy" is a crime," tweeted Iranian journalist Golnaz Esfandiari, reacting to the arrests. Many Iranian users on Twitter were using #freehappyiranians to call on the Iranian authorities to release those arrested in connection with the video.

Pharrell reacted to the news by posting on Facebook: "It is beyond sad that these kids were arrested for trying to spread happiness."