China has protested against Taiwanese President Chen Shui-bian's plans to attend Pope John Paul II's funeral.
It comes amid speculation Taiwan could lose its links with the Holy See
A Chinese spokesman expressed "strong dissatisfaction" at Italy for granting Mr Chen a visa to go to the Vatican.
Italy has diplomatic ties with Beijing, rather than Taiwan, which China sees as part of its territory.
Mr Chen's visit comes amid speculation the Vatican is ready to switch allegiance to China, after their ties were severed in 1951.
China's foreign ministry confirmed the country would not send any representative to the funeral.
Spokesman Qin Gang also complained that President Chen would use the trip to the Vatican to promote his goal, as Beijing sees it, of formal independence for Taiwan.
"His real intention is to take this opportunity to engage in secessionist activity and create 'two Chinas or one China and one Taiwan,' which is what we are opposed to," he said.
The deputy head of China's state-approved Catholic organisation, the Chinese Catholic Patriotic Association, was also angry about the move.
"The decision to let Chen Shui-bian attend has hurt the feelings of the Chinese people, including five million Catholics," said Liu Bainian.
If Mr Chen goes ahead with his trip, he will become the first Taiwanese president to visit the Vatican - one of only 25 nations that officially recognises Taipei diplomatically, and the only one in Europe
He is scheduled to leave Taipei on Thursday for Rome, and stay in the Vatican until after Friday's funeral.
The BBC's Taiwan correspondent says that while it will be a short visit, it is something of a propaganda coup for President Chen.
Television pictures will show him taking part in an event alongside statesmen from around the world, and in Taiwan it will be seen as an important step in the island's campaign to be recognised as a separate entity from China, our correspondent says.
Policy switch mooted
Since the Pope's death at the weekend, the issue of the Vatican's recognition of Taiwan - and its continuing rift with China - has again come under the spotlight.
On Tuesday, a senior Hong Kong bishop said the Holy See might be ready to cut ties with Taipei in order to establish diplomatic relations with Beijing.
Bishop Joseph Zen said the Vatican could change allegiances if China's communist authorities were "willing to grant real freedom to the Church in mainland China".
China's estimated 13m Catholics are currently forced to attend state-controlled churches or worship in secret.
But Beijing reiterated on Tuesday that it was only willing to re-establish diplomatic links with the Vatican if it cut ties with Taiwan and did not use religion to interfere in China's internal affairs.