The ban comes ahead of the peak season for travel – the month-long Saga Dawa festival began on Monday – and is likely to be seen as a response to growing unrest at Chinese rule.

Last month two Tibetans set fire to themselves outside Jokhang temple in Lhasa, a Buddhist shrine that receives thousands of visitors each day. Although at least 37 people have carried out similar protests since March last year, it was the first recorded self-immolation attempt in Lhasa, a popular destination for foreign tourists.

Several Beijing-based tour operators have since claimed that the Chinese National Tourist Office (CNTO) has told them to stop taking foreign visitors to Tibet indefinitely.

Nobody from the Chinese Embassy in London or the CNTO was able available to comment, but Explore – a British operator whose next tour to the region begins on June 28 – said that a ban could last for the duration of Saga Dawa.

“The rules and regulations surrounding Tibetan permits have changed frequently over recent weeks, with the authorities denying access to smaller groups at various stages,” said Carl Burrows, sales director at Explore. “This week our agents alerted us that this may be extended to a blanket ban on tourist permits for the rest of this month, regardless of the number in the group.”

He said he was hopeful the Chinese government would reconsider its stance, but confirmed that any affected travellers would be offered a full refund.

China has banned foreign tourists from visiting Tibet before, usually during periods of unrest and during religious festivals. Overseas tourists were prevented from travelling to the region briefly last year, and for several months in 2008, following violent protests in Lhasa, although the ban was lifted before the Beijing Olympics.

Even when foreigners are permitted into Tibet, tours are closely monitored, travellers must apply for a special visa and they will be accompanied by a government-appointed guide. All foreign tour operators must make their arrangements through Chinese firms.

Fionnuala McHugh, who visited Tibet for Telegraph Travel last year, said the recent protests could have encouraged China to act.

“They do this quite often, but not usually during the peak travel period,” she said. “The vast majority of visitors to Tibet are from China, but the government closely regulates overseas tourism to Tibet, and want to control what people see.

“Tourists will inevitably be carrying cameras and phones, and [China] really doesn’t want them – and the world – to see people setting fire to themselves.”

Justin Francis, co-founder of Responsible Travel, which also offers tours to the region, said the exact nature of the ban had yet to be confirmed and urged Chinese authorities to clarify their position.

He added: “Given renewed strains in the political relationship between China and Tibet in recent weeks and marked escalation in protest, this new, seemingly unexplained ban will raise alarms in the back of the minds of travellers and the tourism industry about what is happening on the ground.

“Responsible travellers have always provided a powerful means to bear witness to political upheaval in tourism destinations, and we will continue to advocate the openness of responsible tourism as a means of keeping the international community informed on local issues and interests around the world.”