Tuesday marks the 50th anniversary of the Dalai Lama's flight to India, after a failed uprising against Chinese rule in his homeland, Tibet.  Half a century later, the Chinese government is making it clear it considers the exiled Tibetan spiritual leader a pro-independence figure, who at this time, is still not welcome to return.

China's continued sensitivity to the Dalai Lama was highlighted when it abruptly canceled a major China-Europe summit in December, after the French president met the Nobel peace laureate.

Chinese Foreign Minister Yang Jiechi stressed that for his government, the issue is, and always will be, one of national sovereignty.

Yang says Beijing's differences with the Dalai Lama are not over religious issues, human rights, democracy or culture.  Instead, he says, China sees it as a "major issue" - defending national unity and preventing Tibet from being separated from Chinese territory.

China has accused the Dalai Lama of seeking Tibetan independence.

The Dalai Lama has repeatedly and publicly said he only seeks cultural and religious autonomy for his homeland, amidst reports by Tibetan activists that China is trying to wipe out Tibetan culture.

To guard against possible unrest for the anniversary, Chinese authorities have stepped up police patrols in parts of Tibet and Tibetan areas in western China.

Senior Tibetan official, Legqog, said the intensified security presence is a temporary measure against "possible disruptions by the Dalai Lama's followers and Western "Tibet independence" groups."

A year ago, monk-led protests against Chinese rule in Tibet's regional capital Lhasa turned into violent rioting, in which the Chinese government says 19 people were killed.

Qiangba Puncog, the chairman of Tibet's government, told reporters this kind of violence will not happen again this year.

The Tibet official says most people in Tibet are supportive of the government, and that local authorities have taken what he described as "appropriate defense measures."

In one small largely-Tibetan town in neighboring Sichuan province, one resident - who did not give his name for fear of reprisal - said the presence of Chinese security forces has become a part of daily life.

The resident says it is not convenient to go outside these days, and that food has become more expensive and harder to buy because the soldiers are eating it too.

The Chinese government strictly limits access to Tibet by foreign journalists.  But activist groups report that the heightened tension has not dampened enthusiasm for the Dalai Lama in Tibetan areas in China.  He is considered to be the living head of Tibetan Buddhism.

In one of the most widely reported recent incidents, a monk in Sichuan province's largely Tibetan Aba Prefecture set himself on fire during a prayer festival at the end of February.

Sichuan Province's senior vice-governor Wei Hong told reporters the monk received immediate rescue assistance from the government.

Wei says the monk's parents expressed gratitude.  He says local people think self-immolation is disrespectful of human rights and also Tibetan Buddhist doctrines.  The Chinese official stresses that the government dealt with this incident humanely.

Sharon Hom, of the US-based advocacy group Human Rights in China, says she is not surprised by the Chinese government's attitude.

"If you report someone setting themselves on fire, a Tibetan monk setting himself on fire, I really do think from the authorities' perspective, it's showing that Tibetans are resorting to very extreme behavior," said Hom.

At the same time, she points out that the Chinese government has been consistently denying broader reports of massive crackdowns on Tibetans in China.

The official Xinhua new agency recently ran an eyewitness account from Lhasa.  The reporter, Zhou Yan, observed little friction between the Tibetans and the Han Chinese, who make up the majority of the country's one point three billion people.

Zhou said although most stores were run by Han Chinese, most of the workers were Tibetan.  The reporter said the influx of Han Chinese to the region also has created more jobs in Lhasa for Tibetans, such as shoe polishers and pedicab drivers.

The Xinhua report also said there are "truckloads of People's Liberation Army soldiers" on Lhasa's streets this month.  But it said the troops have been winning local fans by providing free health services and hair cuts.

China considers Tuesday the 50th anniversary of when Chinese liberators brought democratic reforms to Tibet.  Beijing will celebrate the occasion with a holiday it is calling "Serf Liberation Day," which will be marked for the first time March 28.