Indian military officials said Wednesday that negotiations with Boeing to buy helicopters worth $2.4 billion could take up to six months to conclude.

New Delhi last month selected the US aeronautical giant to provide 15 Chinook CH-47F heavy-lift helicopters and 22 AH-64D Block III Apache helicopters for its expanding air force.

"Once the company has been selected, commercial negotiations begin almost immediately," a senior air force official told AFP.

"The duration of the negotiations can vary between three and six months but if it takes longer it does not mean the deal is going bad," said the official, who spoke on condition of anonymity.

Boeing's twin-rotor Chinook was chosen over Russia-based MiL Moscow Helicopter Plant's Mi-26, while the Apache was selected over the Mi-28, the official said, confirming earlier media reports.

There was no immediate official comment from the Indian Air Force or Boeing.

Dow Jones Newswires said the Chinook deal was estimated at $1 billion while the Apache deal was worth $1.4 billion.

The decision marks a significant shift for India away from its traditional arms supplier Russia.

Earlier this year, France's Rafale won a competition to provide 126 combat jets for the Indian Air Force.