BEIJING (AFP) - Chinese video streaming websites have removed four legally licensed United States television shows in a move that could portend "stricter online monitoring", the state-run media reported on Monday.

"From Saturday, popular shows 'The Big Bang Theory', 'The Good Wife', 'NCIS' and 'The Practice' were no longer available on tv.sohu.com, youku.com and v.qq.com," the Global Times said, referring to three popular services and adding that the series were "all purchased legally for viewing in China".

China closely censors all forms of media, from newspapers to foreign films to microblogging posts, in a vast effort to control public discourse and avoid sensitive topics that could undermine the Communist authorities' grip on power.

But it was unclear why these shows, which did not have excessively political or sexual themes that might be considered inappropriate, were removed.

TV series from the US and Britain were "increasingly popular in China" and "importing shows has become big business", the Global Times said.

The removal of such content "may indicate that authorities are imposing stricter online monitoring", it cited film and drama critic Be Chenggong as saying.

But Mr Be added that fans of the shows could easily access them from unauthorised websites anyway.

The government body overseeing media, the State Administration of Press, Publication, Radio, Film and Television, could not be reached for comment.

In a notice in January it vowed to more "seriously implement a system in which shows obtained approval before being broadcast", noting that some online content had been found to violate certain regulations after being broadcast and had to be taken down.