SHANGHAI, Jan 18, 2010 (AFP) - Mobile users in Shanghai caught sending dirty short messages, photos or videos by phone could have their numbers cancelled as part of China's crackdown on pornography, state media reported Monday.

An employee at the Shanghai subsidiary of China Mobile, the world's biggest phone operator by market value, said the company would search for keywords and then forward the offending messages to the police to investigate.

"We will first block the user from sending and receiving messages ... and the police station will then evaluate it," the unidentified employee was quoted in the Global Times as saying If police found the message contained "dirty words", the phone number would be cancelled, said the report.

State media said last week China Mobile users would be banned from sending texts if they are found to have distributed pornography or other "illegal" content by phone.

But this latest report indicates the mobile operator could now go one step further by cancelling phone numbers.

Calls by AFP to China Mobile were not immediately answered.

China Mobile had 518.1 million subscribers at the end of November, according to the latest company figures - accounting for more than 70 percent of the country's mobile phone users.

China strictly censors the Internet and other media, saying it is aimed at curbing pornographic or violent content.

But critics allege the so-called "Great Firewall of China" is used to strangle dissent and curb the spread of political content deemed a threat to Communist Party rule.

More than 15,000 pornographic websites, including over 11,000 mobile WAP sites - websites that users can access via cell phones - were shut down or blocked in 2009, the official Xinhua news agency said last week.

Beijing has vowed tougher online policing in 2010 as a key element of "state security."