Saudi Arabia and Qatar on Monday signed a deal to construct a high-speed rail connecting the Gulf countries’ capitals, marking the latest sign of improved ties between the two nations that were once deeply at odds.

According to a statement in the official Saudi press, the “high-speed electric passenger railway” would connect Riyadh and Doha. The Saudi cities of Al-Hofuf and Dammam are also expected to be on the network.

The train would reach speeds exceeding 300 kilometres per hour and the trip would take roughly two hours between the two capitals. A direct flight between the cities clocks in at around 90 minutes.

The project, set to be completed in six years, expects to serve 10 million passengers per year, the statement said.

The agreement was signed by Saudi Crown Prince Mohammed bin Salman and Qatar’s Emir Sheikh Tamim bin Hamad Al Thani during the latter’s visit to Riyadh.

The deal is just the latest in a series of moves marking the dramatic improvement in ties between the Gulf countries in recent years.

Saudi Arabia and its allies, the United Arab Emirates, Bahrain and Egypt, had cut all diplomatic and transport ties with Qatar in June 2017.

The four nations accused Doha of backing radical extremists and seeking closer ties with Saudi Arabia’s arch-rival Tehran — allegations that Qatar vehemently denied.

Relations were fully restored in January 2021 after a summit in the Saudi desert city of Al Ula.

Prince Mohammed visited Doha in December 2021 for the first time since the thaw in ties, as part of a regional Gulf tour.

Since then, leaders from the two monarchies have met regularly and joined forces to back diplomatic initiatives, including calls for a ceasefire in Gaza. Riyadh also threw its support behind Qatar following Israeli strikes on Doha over the summer.