A price range of 3.90 to 4.70 lira has been set for an initial public offering of Turk Telekom, valuing the operator at up to 16.45 billion lira ($12.9 billion), the Privatisation Administration said.

The administration said in a circular published on Sunday that book-building would take place between April 28 and 30.

Turk Telekom, which was partly privatised in 2005, is listing a 15 percent stake or 17.25 percent including an over-allotment option. The government is pressing ahead with the deal despite a 22 percent slide on Istanbul's main stock index this year which has prompted several IPOs to be postponed.

A 16.45 billion lira market value, or $12.85 billion at current conversion rates, compares with the $11.91 billion at which the company was valued in 2005 by the first deal in its privatisation process, when Dubai-based Oger Telecom paid $6.55 billion for a 55 percent stake.

At the top of the price range, the sale of a 15 percent stake would raise 2.47 billion lira, well below revenues of 3.9 billion lira which the government had forecast in this year's budget.

The deal had been expected to be the Istanbul stock exchange's biggest offering but the price range indicates it could end up on a par with Halkbank's IPO last year, which was worth about 2.5 billion lira.

 Turk Telekom, whose mobile business Avea is the third operator in fast-growing Turkey, had revenue of 9.2 billion lira last year and net profit of 2.5 billion, according to the circular.

Sixty-five percent of the offering will be aimed at foreign institutional investors. Deutsche Bank and Garanti Securities, part of Garanti Bank, are advising on the offering. -Reuters