Dhaka - Dhaka has alleged three Indian ships illegally entered Bangladesh's territorial waters to carry out hydrocarbon exploration activities in the Bay of Bengal, media reports said Friday.

Foreign ministry officials said the government protested the Indian intrusion into Bangladesh's maritime boundary and on Thursday night dispatched a naval frigate to the area, asking the Indian ships to go back to their territory.

Bangladesh's Foreign Secretary, Touhid Hossain, said he had information that Indian ships entered Bangladesh waters. However, he refused to give details.

The Indian survey vessels started seismic survey activities some 140 nautical miles south-west of Mongla seaport, a Bengali language newspaper reported, quoting a navy source.

The alleged intrusion comes just three days ahead of Bangladesh's general elections, slated for Monday.

Bangladesh is yet to demarcate its maritime boundary in the mineral-rich Bay of Bengal with its neighbours - India and Myanmar - making it difficult to conduct oil and gas exploration.

India and Myanmar have already offered international oil giants rights for mineral exploration in their territories, which Bangladesh says partly overlap with its own territorial waters.

In November, tensions rose between Dhaka and Yangon over Myanmar's attempts to explore oil and gas in waters disputed by Bangladesh, prompting the two sides to send warships to the bay.

After almost two weeks of disagreement over offshore oil and gas exploration in the bay, the two sides agreed to stop mineral searches in the disputed waters until an agreement is signed finalising the demarcation of the maritime boundary between Bangladesh and Myanmar. (dpa)