China has angered India by issuing unorthodox visas to two Indians from a border state claimed by Beijing, the latest flare-up of a territorial dispute festering between the Asian giants.

India's foreign ministry said on Thursday it had seen reports that an Indian athlete and his coach from the remote northeastern state of Arunachal Pradesh, on the Chinese border, were issued visas on papers stapled to their passports. Chinese visas are normally stamped into Indian passports.

The state is one of the biggest issues of contention between the fast-growing Asian nations who are competing for global influence and resources.

China and India still claim vast swathes of each other's territories along their 3,500 km (2,173 mile) Himalayan border which has largely remained peaceful since a 1962 war, but their unsettled border remains the biggest single impediment to better relations.

We have unequivocally conveyed to the Chinese side that a uniform practice on issuance of visas to Indian nationals must be followed, regardless of the applicant's ethnicity or place of domicile, the Indian foreign ministry said in a statement.

The ministry had also issued a travel advisory cautioning Indian citizens that Chinese paper visas, stapled to the passport, were not considered valid for travel out of the country.

In the past, China has refused to issue visas to Indians from Arunachal Pradesh saying they did not need permission to travel to China.

In 2009, India protested against a Chinese policy of issuing different visas to residents of Kashmir, a state which India and arch-enemy Pakistan rule in part but claim in full. Beijing supports Pakistan's claims to Kashmir.

A few weeks ago, Chinese Premier Wen Jiabao visited India in an effusive display of warmth that, however, failed to lift the veil of suspicion between the two nations or resolve their border disputes.

China's support for Pakistan, which backs separatists in Kashmir, has not helped defuse tensions. Beijing resents the presence of the Dalai Lama, the exiled Tibetan leader, in India.

Despite decades of mistrust, China is now India's biggest trade partner. The value of bilateral trade was expected to pass $60 billion this year, a 30-fold increase since 2000, underlying the importance of better relations between the Asian neighbours.

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