The attack on the Norwegian-owned merchant vessel, M V Maud, flying the Liberian flag, took place about 225 nautical miles east of Aden around 1300 hours on Thursday, sources said.
The Indian warship immediately responded to the distress call and advised the vessel to increase speed and carry out evasive manoeuvres to avoid getting boarded. Simultaneously, a helicopter with marine commandos took off and started closing in on the threatened vessel, a senior Indian Navy official said.
The visibility being low, it was possible that pirates might not have sighted the warship and the helicopter. The helicopter crew fired warning shots to deter them from boarding the ship, he said.
Following this, two pirates, who were attempting to clamber up the merchant vessel, fell into the water.