ALGIERS - Algeria, Nigeria and Niger have signed a memorandum of understanding to build a natural gas pipeline across the Sahara desert, Algeria's energy minister said on Thursday.

The three countries had in June agreed to revive the decades-old talks over the project, a potential opportunity for Europe to diversify its gas sources.

The pipeline is expected to span 4,000 kilometers, according to Algeria's Ennahar TV.

The Trans-Saharan gas pipeline is an estimated $13 billion project that could send up to 30 billion cubic metres a year of supplies to Europe.

The idea was first proposed more than 40 years ago and an agreement signed between the countries in 2009, but progress stalled.

(Reporting by Lamine Chiki in Algiers and Lilian Wagdy in Cairo; Writing by Nadine Awadalla; editing by David Evans)