Italy, Japan and Britain could open up a programme aimed at developing an advanced fighter jet to other countries, but at a later stage, Italy's defence minister said in an interview published on Friday.

The three countries in December signed an international treaty to set up the Global Combat Air Programme (GCAP) - the first major defence industry collaboration merging the separate next-generation fighter efforts of the countries.

"We will not open (the programme) to others until the initial phase will be closed," Guido Crosetto told Italian daily Il Corriere della Sera, adding many countries were interested in entering but without directly answering a question on interest from Saudi Arabia and the United Arab Emirates.

"Afterwards, with everyone's agreement, we could widen it to other countries," Crosetto added.

The aim is to see the combat aircraft in flight by 2035. The joint development phase is expected to begin in 2025.

Reuters previously reported that the GCAP may welcome other nations as junior partners, with Saudi Arabia among the contenders as it would bring money and a lucrative market to a project expected to cost tens of billions of dollars.

(Reporting by Giulia Segreti, editing by Alvise Armellini)