For nearly 30 years, the two countries have argued over control of New Moore Island, a strip of rock about two miles long and 1.5 miles wide.

But oceanographer Sugata Hazra says satellite imagery and sea patrols of the coastal area known as the Sunderbans no longer register the island, which has been submerged by the rising water.

Bangladesh refers to the island as South Talpatti.

Mr Hazra, a professor at Jadavpur University in Kolkatta, said: "What these two countries could not achieve from years of talking has been resolved by global warming."

Until 2000, the sea level rose about 0.12 inches a year, but over the last decade it has been rising about 0.2 inches annually, he said.

Another nearby island, Lohachara, was submerged in 1996, forcing its inhabitants to move to the mainland, while almost half the land of Ghoramara island is underwater, he said. At least 10 other islands in the area are at risk as well.

"We will have ever larger numbers of people displaced from the Sunderbans as more island areas come under water," he said.

There were no permanent structures on New Moore, but India sent some paramilitary soldiers to its rocky shores in 1981 to hoist its national flag.

The demarcation of the maritime boundary - and who controls the remaining islands - remains an open issue between the two South Asian neighbours, and the disappearance of the island does nothing to resolve it, said an official in India's foreign ministry.