As Beijing's official media condemned what it called a "petty" decision, a senior official in New Delhi confirmed three journalists would have to leave India within the week at the security services' instigation.

"They had come to the adverse attention of the security agencies," the official told AFP on condition of anonymity.

"They were doing activities that were not compatible with their journalist status."

The official said the trio were not being officially expelled but their annual visas would not be renewed and they would have to leave by July 31.

There was no official word on why the reporters had fallen foul of the Indian authorities.

But a report in Monday's Hindustan Times said two of them had visited Tibetan settlements in the southern state of Karnataka last year, without securing a permit from the home ministry and while using false identities.

"The journalists had not taken the PAP (Protected Area Permit) for visiting the camps but their real identities were detected when they reached there," an official told the newspaper.

India is home to thousands of Tibetan refugees who fled their Himalayan homeland when China sent in troops in 1951 to quell an uprising.

Many of those who took flight -- including Tibetan spiritual leader the Dalai Lama -- settled in and around the Indian northern town of Dharamsala where a Tibetan government in-exile functions.

Others live in designated settlements elsewhere in the country that are off-limits to foreigners, such as the one in Karnataka which is home to around 40,000 Tibetans.

The exile community held elections in April for the leadership of the Dharamsala government -- an organisation that China has consistently refused to recognise.

India's hosting of the exiled government is a long-running thorn in relations between the two neighbouring countries.

Often prickly tensions between the world's two most populous countries have also been inflamed recently by China's blocking of India's attempt to join a 48-nation nuclear trade group.

An editorial on Monday in Beijing's state-run Global Times newspaper said there was "speculation" that the decision on the journalists' visas was India's "revenge against China" over the nuclear group veto.

"If New Delhi is really taking revenge due to the NSG (Nuclear Suppliers' Group) membership issue, there will be serious consequences," it added.

The same editorial also said Beijing "should make a few Indians feel Chinese visas are also not easy to get".