Pornography spread on cell phone networks has seen a resurgence recently, the Internet information safety group under the Chinese Academy of Sciences (CAS) said in a report released on Thursday.

The trend is the latest obstacle to a crackdown by authorities on porn being disseminated through wireless application protocol (WAP) sites on mobile phones.

Some telecom operators should play a role in stemming the distribution of porn through the networks, the report said.

"I don't know why porn pages can be seen again," Zeng Hai, a 17-year-old high school student in Guangdong province, told China Daily on Friday.

Zeng said a website which included many lewd pictures appeared when he surfed on the Net using his cell phone on May 28.

Zeng said some of his classmates also discovered that pornographic websites that were previously blocked were accessible again.

Huge profits from charging pornographic sites?are the main reason behind the resurgence of the lewd material, despite repeated crackdowns by the government, the report said.

A nationwide campaign by nine Chinese ministries that started last December to crack down on mobile porn closed more than 140,000 illegal websites as of the end of March this year, the website administered by the National Office Against Pornographic and Illegal Publication reported.

But the CAS report said that 76 mobile websites were found with lewd content after a sample of 1,000 sites from May 21 to 27.

Among the illegal websites, 14 were registered before this year, six were registered this January and two were registered in February. But the number jumped to 22 in March and 18 in April.

More than 12.5 million visits were made to those websites every day, the report said.

China Mobile, the country's largest wireless telecom operator, announced last November it would suspend cooperation with all WAP business promotion partners and clean up porn sites, Xinhua News Agency reported.

But five telecom operators the CAS report surveyed were all found providing WAP service to mobile pornographic sites as of last month. Those operators included China Mobile's four branches in Beijing and Shanghai cities, as well as Zhejiang and Shandong provinces, and the China Unicom Beijing Company.

Investigations found that the mobile service providers did not fully cut off the profit chain between them and WAP sites. They are still "secretly providing services to porn sites", the report said.

Li Qiang, a researcher with the Institute of Policy and Management at the Chinese Academy of Sciences and a contributor to the report, told China Daily that more concrete measures should be taken to crack down on the spread of lewd material on mobile phones.

"Telecom operators that violate laws or regulations should be held legally accountable for their actions," Li said.

"The system should be carried out as soon as possible."