Japan's Daiichi Sankyo Company Ltd is selling shares worth up to $3.6 billion in Indian drugmaker Sun Pharmaceutical Industries Ltd , setting it on course to retreat from India after a rollercoaster seven years.

Daiichi Sankyo bought India's Ranbaxy Laboratories in 2008, betting on growing global demand for generic drugs, but found itself saddled with a company battling complaints and sanctions from the U.S. Food and Drug Administration (FDA).

Mumbai-headquartered Sun Pharma, India's largest drugmaker by sales, agreed to buy Ranbaxy from Daiichi Sankyo for $3.2 billion in April 2014. As part of that deal, Daiichi Sankyo got an 8.9 percent stake in the new Sun Pharma.

Daiichi Sankyo kickstarted the sale of the Sun Pharma stake, according to a person directly involved in the deal and a marketing term sheet seen by Reuters, through accelerated book building.

The sale comes after Sun Pharma completed the acquisition of Ranbaxy in March.

In an exchange filing, the Japanese drugmaker said its board had approved the sale of all or part of the Sun Pharma stake. It gave no reason for the sale, but added the existing business partnership with Sun Pharma would remain unchanged.

"From the perspective of the improvement of corporate value, Daiichi Sankyo has performed a review of the Sun Pharma shares and reached a conclusion to sell the shares entirely or partially," it said.

Daiichi Sankyo said it would disclose the financial details related to the Sun Pharma stake sale when it announces results for the fiscal year that ended on March 31.

Daiichi Sankyo's decision to sell Ranbaxy last year came against the backdrop of a slew of sanctions imposed by the FDA on the Indian company over concerns about manufacturing processes at its India plants.

At the time of the Ranbaxy sale to Sun Pharma, the value of the Japanese firm's investments in the country had halved since it bought control, as the regulatory problems had triggered a sharp fall in Ranbaxy's share price.

The Sun Pharma shares are being sold in the indicative price band of between 930 rupees and 1,043.80 rupees apiece, according to the term sheet, a discount of as much as 10.9 percent on Sun Pharma's stock price at the end of the trade on Monday.

Sun Pharma shares closed on Monday at 1,043.80 rupees.

A spokesman for Sun Pharma in Mumbai declined to comment on Daiichi Sankyo's stake sale.