The country's biggest refiner Indian Oil Corp Ltd said on Wednesday that Iran has not ruled out participating in a refinery expansion project at an Indian Oil subsidiary.

Indian Oil's chairman Sanjiv Singh said that Iran had not said no to participating in the expansion of Chennai Petroleum Corp Ltd, a south India-based 20,000 barrels per day refinery.

Iran's participation has been questioned after India cut down its Iranian crude oil imports following US sanctions.

Chennai Petroleum plans to invest over $5 billion for modernisation and expansion.

Naftiran Intertrade, the Swiss subsidiary of National Iranian Oil Company, holds a 15.4 percent stake in Chennai Petroleum, while Indian Oil has about a 52 percent share.

Singh said a detailed feasibility report for the expansion has yet to be prepared.