China must also manage the Internet to promote the Communist Party’s religious theories and policies, the official Xinhua news agency cited Xi as saying.
“We must resolutely resist overseas infiltration through religious means and guard against ideological infringement by extremists,” Xi was quoted as saying at a two-day national working conference on religion that ended on Saturday.
The ruling Communist Party says it protects freedom of religion, but it keeps a tight rein on religious activities and allows only officially recognised religious institutions to operate.
The government is concerned about what it sees as the growing influence by Islamists in the Xinjiang region in the far west where hundreds of people have been killed over the past few years in violence between members of the Muslim Uighur community and majority Han Chinese.
Officials there have stepped up regulations banning overt signs of religious observance, like veils or beards.
Separately, some Chinese Christians say authorities are limiting their activities and taking down crosses on churches in coastal Zhejiang province.
Authorities have said crosses are removed because they violate regulations against illegal structures.
Protests broke out in 2014 in the heavily Christian city of Wenzhou, also in Zhejiang, over the government’s cross demolition campaign.
In January, authorities also said a Christian pastors was being investigated for suspicion of embezzling funds. The investigation came after the pastor opposed the campaign to remove crosses.
Communist party members must adhere to Marxist principles and remain “staunchly atheist”, Xi said in his remarks.