Bulgaria launched the construction of a five-kilometre section of the Sofia underground railway worth 136.1 million levs ($89.2 million/69.5 million euro), the transport ministry said.
The project is co-financed by the EU-funded operational program Transport, the transport ministry said in a statement on Wednesday.
The new underground railway section will link the city with the Sofia international airport. Its construction should be completed in early 2015.
Another section of the underground railway linking the southeastern residential districts of Mladost 1 and Mladost 4 in Sofia is also expected to be completed by then.
Sofia's underground railway network is currently 31 km long and has 27 stations.