Peruvian government warned it must be consulted over plans to locate airport near world heritage sites that include the Inca citadel and Sacred Valley

Unesco has sent a letter to the Peruvian government demanding information about the construction of a new airport near Machu Picchu and what impact it could have on the Inca citadel, the country’s biggest tourist attraction and a world heritage site.

The letter, which has not been made public, reminds Peru of its obligation to protect its world heritage sites and directly refers to Chinchero, the historic village in the Sacred Valley, near the town of Cusco, where the controversial new airport is being built – to the horror of archeologists.

The missive insists that Peru must coordinate with Unesco, the United Nations’ cultural agency, on any construction that could affect Machu Picchu and Cusco’s historic centre, also a world heritage site. A spokesperson for Peru’s ministry of culture said it would reply by 25 August, the date set by Unesco to receive an official response.

It is not the first time Unesco has sent Peru a warning about Machu Picchu. It threatened to place the famous ruins on a list of world heritage sites in danger in 2017 over fears overcrowding could damage the structure.

As a result Peruvian authorities put controls on the flow of tourists – an average of 5,000 a day in summer, more than double the Unesco-recommended limit – by dividing visits to the site into morning and afternoon shifts. Around 1.5m tourists visited Machu Picchu in 2017 and visitor numbers continue to increase. The Peruvian government hopes a second airport for Cusco, with direct flights from Miami and Buenos Aires, could nearly double the number of tourists.

The Peruvian president, Martín Vizcarra, has vowed that the airport, set for completion in 2023, must go ahead. He used his recent Peruvian independence day speech to allay fears that the construction would affect the “archaeological, natural, historical and cultural legacy of Cusco”. On a visit to the site this week, Peru’s transport minister, María Jara, said “nothing would stop” the airport’s construction.

While tour operators and hoteliers mostly agree that Cusco, Peru’s principal tourist destination, needs a second airport, there is debate about whether the 600-year-old Inca site of Chinchero is the best location for it. Juan Stoessel, general manager of the Casa Andina hotel chain, argues the chosen location would allow planes to land and take off from both sides of the runway – unlike the alternative sites in the mountain region – making it a hub for flights from the main cities in the region.

“Cusco receives around 3.5m tourists a year, which is a very low number compared with other world-class tourist destinations,” said Stoessel, adding that nearby archeological sites such as Ollantaytambo, Choquequirao and Vilcabamba needed better management.

But Marisol Mosquera, founder and CEO of Aracari Travel, said: “It breaks my heart to see one of the most monumental and gorgeous landscapes in the Andes being defaced in the name of ‘progress’. Our goal was to promote sustainable, low-impact, high-quality tourism. Now the destination is being destroyed.”

A spokesperson for Unesco Peru said it could not comment as matters relating to world heritage sites were dealt with by the body’s Paris headquarters.