BEIJING, April 10 (Xinhua) -- China's leading task-force fighting pornography has said the Internet is its "main battleground" and it will maintain high pressure on such activities.

The National Office Against Pornographic and Illegal Publications on Tuesday reported its work progress in the first quarter of 2018.

More than 530 cases concerning online porn and illegal publication have been investigated across the country, it said.

While a larger number of cases were investigated offline, the office said fighting online obscenity remained its work focus.

The office said two new campaigns were launched this year to clean the cyberspace and protect minors.

It detailed 13 prominent cases targeted by the campaigns.

In one case, 19 people were convicted by a local court in eastern Shandong Province to jail terms ranging from one to four years for operating a website allowing members to upload and download porn videos and photos, which profited by nearly 70 million yuan (11 million U.S. dollars) through advertisement.

In another case, 22 people were arrested in northern Hebei Province for using overseas servers to run membership-only porn websites, which held tens of thousands of obscene video clips.

In a third case, eight were arrested in eastern Jiangsu Province for spreading porn via a mobile phone app.