AGRA, Oct 21: Authorities in Uttar Pradesh state have launched an urgent investigation after historians reported that one of the minarets of the Taj Mahal is tilting dangerously, an official said.

A committee of experts is investigating whether the drying out of the nearby Yamuna river could have affected the 17th-century white mausoleum's foundations, the state government official said on Wednesday. They are to report back within a week, said the official.

The Taj Mahal, with four slender minarets, sits on the banks of the Yamuna river.

Agam Prasad Mathur, a historian and former vice chancellor of Agra University, said the Yamuna river bed must once again be filled to prevent the minaret from tilting further.

"It was during a survey conducted by British colonial rulers in 1940 when it was found that the minaret had tilted by 4.5 inches (11 centimetres). Another survey in 1965 found the tilt had increased by five inches (12.5cms)," said Mr Mathur.

"With passing time, the tilt must have increased and needs to be determined," he said, adding that the Yamuna river needs to be full to maintain the monument's balance.

"The foundation of the Taj Mahal is laid on a hillock and is based on wells underneath which require moisture from the Yamuna river. Regular flow of water in the Yamuna is a must...the tilting could be a fallout of scarcity of water in the river," he added.

He explained that the Taj stands on a raised platform and the four 41.6 feet (12.6 metre) minarets at each corner give it balance. The minarets have deliberately been constructed to tilt slightly to prevent them from crashing onto the tomb in the event of an earthquake.

Ram Nath, former head of history at Rajasthan University, sounded a similar warning.

"Dangerous tilts in its minarets, first noticed in 1942 and mentioned in various reports, have continued to increase over the years," Mr Nath told the Hindustan Times. "They are caused by the dry river bed."

Lawyer Ajay Agarwal said he would urge the Supreme Court to order the state government to construct a barrage to ensure the water level in the Yamuna stayed constant to prevent the minaret from tilting further.

"Immediate action is needed to save the Taj Mahal," said Mr Agarwal.

The Archaeological Survey of India has played down the perceived danger.

"We do have regular surveys done by concerned authorities after every four years at the Taj Mahal and any such anomaly in a minaret of the Taj could not have gone unnoticed," said a senior survey official.

The Taj Mahal was given a facelift two years ago to remove decades of grime and pollution stains.

Last month, marathon celebrations were held in Agra to mark the 350th anniversary of the construction of the monument.

Around 2.2 million Indians and 800,000 foreigners last year visited the Taj Mahal - far more than any other tourist site in India.

Some 20,000 workers toiled for over 20 years to build the Taj in an age of opulence when the dynasty mined precious gems to fund construction of grand projects.-AFP