Temperatures hovered this week at 45 Celsius (115 degrees Fahrenheit) in the city, 200 kilometres (124 miles) south of New Delhi, as a heat wave that has killed 60 people nationwide in the past week dragged on.

The Yamuna River, which runs behind the 17th-century white Mughal tomb, was dry and Agra's chief archaeologist Doraiswamy Dayalan said he was worried that dust from the nearby desert and factories would turn the marble yellow.

"The dry river allows dust and suspended particulate matter to rise and flow in the air and slam into the monument's surface," said Dayalan, of the Archaeological Survey of India which cares for the Taj.

"If water returns to the Yamuna then there will be less suspended matter in the air," Dayalan said, adding that he was praying the annual monsoon rains arrived by the end of June.

Ajay Taneja, a chemistry professor at Agra University who monitors the tomb built by Mughal emperor Shah Jahan in memory of his second wife Mumtaz Mahal, agreed, saying: "This is not good for the health of Taj."

Dayalan, however, said the Taj had been built to deal with the heat that bakes India every summer.

"The thickness of the walls of the Taj are two to three meters (6.6 to nine feet) with marble forming its surface while its core is made up of lime, mortar and brick.

"The moisture in the core evaporates in hot weather and cools the outer surface and thus maintains an equilibrium," he said.

The heat had prompted him to install special insulation on the monument's floor to prevent tourists' feet from blistering as regular shoes are banned inside the monument.

The Taj Mahal underwent a facelift three years ago to remove decades of grime and pollution stains.

Last September, celebrations marked the 350th anniversary of the construction of the monument, which is flanked by four slender minarets and a lavish lawn.

Almost three million domestic and foreign tourists annually visit the Taj Mahal, more than any other tourist site in India.

Some 20,000 workers toiled for over 20 years to build the tomb in an age of opulence when Muslim rulers mined precious gems to fund construction of grand projects.

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