Japanese drug maker Daiichi Sankyo Co is yet to receive Indian regulatory approval for an open offer for Ranbaxy Laboratories, and so will not launch it on Aug. 8 as previously planned, the offer's manager said on Thursday.

Daiichi, which was to launch the offer for 20 per cent of Ranbaxy, will announce a "revised schedule of activities" after it receives approval from the markets regulator, ICICI Securities said in a newspaper advertisement.

Daiichi agreed in June to acquire 34.8 per cent from Ranbaxy's founding family and was required to make an open offer for a further 20 per cent at 737 rupees per share. If the offer is fully subscribed, Daiichi's stake will rise to 58.09 per cent.

The offer was scheduled to close on Aug 27.

Shares in Ranbaxy, India's leading drug maker by sales, had fallen this month after uncertainty over a US investigation into allegations the company had introduced adulterated and misbranded drugs. Shares in Ranbaxy closed at 492.75 rupees on Wednesday.

The two companies have said the deal was "binding and final".