Cengiz Insaat, which had promised to execute the project for EUR 89.3 million in 2018, now issued a bid worth EUR 99.6 million, DARS announced after opening the bids on Thursday.

Cengiz is followed by Greek J&P Avax with EUR 115 million, and Slovenia's Kolektor CGP, which has partnered with Slovenian engineering company Riko and Turkish company Yapi Merkezi to offer to build the tube for EUR 121 million.

The fourth lowest bid, worth EUR 121.5 million, was submitted by Implenia Österreich in partnership with Implenia Switzerland and Slovenia's CGP Novo Mesto, and the fifth, worth EUR 122.2 million by Slovenia's Gorenjska Gradbena Družba in cooperation with Czech builder Metrostav, which had been the second lowest among nine bidders in 2018.

Bosnia's Euroasfalt and its Slovenian partner Cestno Podjetje Ptujm, which had been among the six bidders invited by DARS into the new round of talks and bids, has not submitted a bid this time.

The bids are now to be examined and the procedure is continuing after the National Review Commission - which annulled the original awarding of the deal to Cengiz with the argument the Turkish company had made subsequent changes to their offer - rejected the call by Kolektor CPG, Yapi Merkezi and Riko to halt the new stage of the procedure.

While Austria is already in the midst of building its portion of the 8-kilometre tunnel, the project has been stuck in the tender stage in Slovenia since it began in 2017, having seen a number of appeals processed by DARS as well as the National Review Commission.