CCRA, Sept 27 (Reuters) - Ghana's debt-ridden state-run Ghana National Petroleum Corporation (GNPC) has laid off 80 percent of its staff as part of a major restructuring, its chief executive said on Thursday.

Ofori Quaah, who described the company as ``broke,'' said a total of 389 staff had been laid off and that GNPC would now concentrate on its core activities of promoting petroleum and gas exploration and production.

In the past GNPC has also been involved in telecoms, banking, gold and salt production as well as cocoa plantations.

``We've already scaled down substantially from where we were, say, three or four years ago. We want to concentrate on our core business,'' Quaah said.

Former chief executive Tsatsu Tsikata, who ran GNPC for 15 years, has been put under official investigation and forensic audit last month.

He has been accused by members of the government of overstretching the company's resources across too many sectors and saddling it with huge debts. Tsikata rejects the criticisms.

Government officials say GNPC owes some $26 million to Credit Suisse and Union Bank of Switzerland UBS , both of whom are demanding repayment.

Switzerland's Societe Generale de Surveillance won a ruling in a British court in June to have GNPC's Discoverer 511 drillship sold to defray a debt of $47 million.

Government officials also say the company spent $62.5 million to buy and refurbish six rigs and other marine assets, but the units have not been put into operation.