New Delhi (AFP) - India has sent warships and stepped up aerial surveillance in strategic Gulf waters, the Press Trust of India reported on Thursday, with global tensions rising in the region.

"INS Chennai and INS Sunayna have been deployed in the Gulf of Oman and the Persian Gulf to undertake maritime security operations," the navy said, quoted by PTI.

The aim is "to re-assure the Indian-flagged vessels operating/transiting through the Persian Gulf and the Gulf of Oman, following the maritime security incidents in the region," the navy said.

Two Indian warships will help to reassure Indian-flagged commercial vessels in the tension-plagued Gulf region -- an Indian guided missile destroyer (C) is pictured on a previous mission (AFP Photo/TED ALJIBE)

US President Donald Trump on Thursday said Iran made a "big mistake" by shooting down a US spy drone. The Pentagon said the downing occurred in international air space but Iran's Revolutionary Guard Corps said the drone had violated Iran's air corridor.

Washington had already accused Iran of carrying out attacks on tanker vessels in the Strait of Hormuz area, which links the Gulf and the Gulf of Oman, and through which much of the world's oil passes.

"Aerial surveillance by IN aircraft is also being undertaken in the area," India's navy said, according to PTI.

India's ambassador to Washington said in May that his energy-hungry nation had ended all imports of oil from Iran, in response to threatened US sanctions.