Bulgaria has extended the deadline for bids in a tender to run and operate Sofia airport by a month to Nov. 18 due to increased interest in the process, Transport Minister Ivailo Moskovski said on Monday.

The government launched the tender to operate the Balkan country's main airport for 35 years in May, in a process it expects to bring some 1.2 billion levs ($689 million) into state coffers.

"The deadline has been extended by a month following a request by three companies that are interested in the deal," Moskovski told reporters. He did not elaborate.

The extension will also compensate for a temporary halt to the process following a complaint to the country's competition watchdog by a consortium that built a runway at one of the terminals. That complaint was overturned in late June.

In August, Turkish Limak Holding said it was planning to bid for the airport.

German airport operator Fraport, which has a 60 percent stake in a venture operating Bulgaria's two Black Sea airports, will look closer at the tender to see if it would be viable to expand in the country, its spokesman said on Monday.

Prior to launching the tender, Moskovski said operators of airports in Zurich, Lyon, Dublin and London Heathrow, as well as firms from Qatar and China, had expressed an interest.

The airport, which was used by more than 4 million passengers last year, is operated by the state. Moskovski said he expects a deal can be done by the end of the year. – Reuters