FILE PHOTO: Red flags fly near a security camera on Beijing's Tiananmen Square Thomson Reuters BEIJING (Reuters) - China is facing heightened threats from foreign infiltration via religion and from the spread of extremism, a top official for religious affairs said on Tuesday, after strict new rules were passed to manage religious practice in the country.

President Xi Jinping has emphasized the need to guard against foreign infiltration through religion and to prevent the spread of "extremist" ideology, while also being tolerant of traditional faiths that he sees as a salve to social ills.

China's parliament last week passed updated rules to regulate religion so as to bolster national security, fight extremism and restrict faith practiced outside state approved organizations. The new rules take effect in February.

Wang Zuoan, the head of China's religious affairs bureau, said the revision was urgently needed because "the foreign use of religion to infiltrate (China) intensifies by the day and religious extremist thought is spreading in some areas."

"Issues with religion on the internet are starting to break out ... and illegal religious gatherings in some places continue despite bans," he added, writing in the official paper of the ruling Communist Party, the People's Daily.

Wang said that freedom of religious faith is protected by the new rules.

"At the same time, freedom of religious faith is not equal to religious activities taking place without legal restrictions," he added.

Religion within China needed to be "sinicized", a term officials use to describe the adjusting of religion to fit Chinese culture as interpreted by the Party.

"These rules will help maintain the sinicization of religion in our country ... and keep to the correct path of adapting religion to a socialist society," he said.

China's five officially sanctioned religions - Buddhism, Taoism, Islam, Catholicism and Christianity - vowed to fight "desinicization" at a forum on the topic held in Beijing last week, according state media.

China has seen a revival of religious practice in recent decades after faith was effectively banned during the Cultural Revolution in the 1960s.

Official estimates put the number of believers at around 100 million, but scholars argue that the real number could be many times higher, due to many believers being unregistered with authorities.

China requires places of worship to be registered with authorities, but many believers shun official settings in preference for private gatherings often known as "underground" churches.

(Reporting by Christian Shepherd; Editing by Richard Pullin)