Four transnational child porn websites have been shut down and more than 250 suspects arrested in a joint operation undertaken by Chinese and foreign police, according to the Ministry of Public Security.

The move was initiated by Chinese and the U.S. police and involved police from 15 other countries as well as Hong Kong, Macao and Taiwan.

Since the operation began in April, more than 180 suspects have been seized for maintaining child porn websites on the Chinese mainland, 60 in Hong Kong, Macao and Taiwan. The U.S. police has shut down websites involved and arrested two suspects.

Suspects overseas are under investigation in accordance with local laws and regulations.

According to the ministry, in September last year, "Zhengjiutianshi" or "to rescue angels," one of the child porn websites, was spotted by the U.S. police and reported to the Chinese police.

Videos, pictures and texts in the website amounted to four TB, which normally takes 48.5 days to download.

The ministry said that the crackdown on the chain of child porn sites has been a successful operation thanks to the international cooperation of police forces.

The ministry will continue to strengthen cooperation with foreign countries to vigorously fight transnational illegality, including online pornography, swindling and computer hacking.

Chinese police has established cooperation with their counterparts in 83 countries and regions and set up 65 hotlines with the police organs in 44 countries, the ministry said.

Chinese police liaison officers have also been sent to embassies and consulates in 23 countries, including the U.S., the United Kingdom and Russia, to beef up cooperation.