Three young Saudis who posted online a video on poverty in the oil-rich kingdom have been detained after an opposition television aired part of their documentary, activists said on Wednesday.

Firas Baqna, Khalid al-Rasheed and Hussam al-Darwish were arrested on Sunday by police in Al-Sahaba district, north Riyadh, after London-based Al-Islah television aired part of their YouTube series entitled "Malub Aleina" ("We are being cheated"), activists said, requesting anonymity.

Al-Islah channel is the mouthpiece of the banned Movement for Islamic Reform in Saudi Arabia, led by Saad al-Faqih.

One rights activist said authorities suspected the three young men "were receiving finance from the channel and were taken into custody for interrogation."

But "they were not charged and are awaiting administrative measures to be released."

The fourth part of the YouTube series, aired on television, was filmed in poor Riyadh neighbourhoods, and featured an interview with a mosque imam claiming vice and drugs were becoming popular in his area due to poverty.

"The aim of the series is to draw attention to social problems, nothing more," said the activist.

The Saudi kingdom, where protests are banned, has a burgeoning young population.