Turkey inaugurated a railway tunnel under the Bosphorus on Tuesday, linking Asia and Europe.

The project, in which Spanish companies played an important role, is being used by Turkey to mark its 90th anniversary as a republic.

The 13.6-kilometer (8.4-mile) tunnel, which has a 1.4-kilometer (0.86-mile) underwater segment, is the first railway link between Europe and Asia south of Russia, and it provides a direct link with the Near East via Iran.

Turkish President Abdullah Gül inaugurated the tunnel as Prime Minister Recep Tayyip Erdogan looked on along with Japanese Prime Minister Shinzo Abe, Romanian Prime Minister Victor Ponta and Spanish Development Minister Ana Pastor.

The official guests were the first to cross the Bosphorus via the new railway tunnel.

"As of today, we have cut the travel time between two continents to four minutes," Erdogan said in an address delivered before the first train made its run through the tunnel.

"Marmaray is a project that will be written about with gold letters in history," the prime minister said.

The tunnel is being inaugurated as the nation marks the 90th anniversary of the founding of the Republic of Turkey in 1923, with the project following in the steps of those who began to modernize the country with expanded infrastructure, the prime minister said.

The tunnel will be used by both commuter trains, which are expected to carry up to 1.5 million people a day in Istanbul, and long-distance freight trains traveling from Europe to Asia.

Spanish construction company OHL was the lead partner in the consortium that won the contract to build the tunnel.

The railway link, about 70 percent constructed by Spanish contractors, cost 932.8 million euros ($1.28 billion), while the entire Marmaray project cost 3.4 billion euros ($4.6 billion).

Spain's Dimetronic, now a unit of German engineering giant Siemens, and Turkish-Japanese consortium TGN were the other partners in the consortium.

Ottoman Sultan Abdulmejid first proposed a tunnel under the Bosphorus in 1891, hiring French engineers to work on the project. EFE