Greece\'s troubled privatisation efforts were dealt a blow on Monday after Russian giant Gazprom unexpectedly withheld bidding on Greek state gas operator DEPA, citing concerns about the company\'s viability. \"We did not receive adequate guarantees that DEPA\'s financial situation will not deteriorate until the deal is concluded,\" Gazprom spokesman Sergei Kupriyanov said in a statement. \"The takeover procedure could last another year after the end of the tender,\" he added. \"The company is already burdened with unpaid customer bills.\" Greek reports said the European Union had reservations about a possible sale to Gazprom which is a key gas supplier to Greece. The Athens stock exchange had earlier closed with losses of 4.69 percent. According to reports, DEPA is owed at least 400 million euros by Greek independent electricity producers and industry. The state privatisation agency (HRADF) said it had pledged to cover debts of up to 180 million euros through to the end of 2015. \"Business activity entails the assumption of certain (business) risk,\" the agency said in a retort to Gazprom. Deputy energy minister Makis Papageorgiou said a new tender would be proclaimed for DEPA, and that Azerbaijan\'s state energy firm SOCAR had tabled a proposal for DESFA, the DEPA subsidiary that handles Greece\'s gas transmission system. SOCAR seeks to buy 66 percent of DESFA, the privatisation agency said. However, Gazprom noted on Monday that a restructuring to separate DESFA from DEPA is still pending. \"The new tender will be held under better conditions,\" Papageorgiou said, according to state news agency ANA, noting that the previous process had been launched amid fears that crisis-hit Greece would be forced out of the euro. Papageorgiou added that SOCAR\'s bid increased chances that gas-rich Azerbaijan will later in June support the construction of the Trans-Adriatic Pipeline -- a project Greece is supporting over the rival Nabucco pipeline that would up to Austria. And the deputy minister said Greece would continue talks with Gazprom on gas prices, which are some 30 percent higher than in other European countries. In a related development, state refiner HELPE said it would immediately begin divesting a 35-percent stake in DEPA. The Greek government had expected a sale after Gazprom chairman Alexei Miller visited Athens three times in the last two months, and even met with Prime Minister Antonis Samaras. In return for two EU-IMF bailouts, Greece has pledged to raise 9.5 billion euros ($12.4 billion) in asset sales by 2016, a target that was originally 50 billion euros. The privatisation drive has had a slow start and revenue goals have been repeatedly scaled back since it began in 2010. The state privatisation agency has also changed three managers in less than a year. Greece must raise 2.6 billion euros ($3.4 billion) in asset sales this year. The state last month sold a 33 percent stake in Greece\'s gaming monopoly OPAP to Greco-Czech consortium Emma Delta for nearly 700 million euros, its largest sale so far. The former Athens airport is also up for sale, in addition to the main electricity provider, the water companies of Athens and Thessaloniki, the state railway company and public buildings.