Rockstar had plans to make Grand Theft Auto: Tokyo, and even carried out a reference trip for the game, techradar has learned.

Rockstar visited the Japanese capital several years ago to assess its potential for a full GTA game, but ultimately pulled the plug on the idea, according to a source close to the company.

Before working on a new game Rockstar carries out reference trips to take pictures, meet locals, and generally get a feel for the area.

Our source said that Rockstar was "serious" about the idea of making a Tokyo version around the time of GTA 3 and Vice City, however the road system was seen to be problematic and became one reason the idea was canned.

In December 2003, Take-Two Interactive actually filed trademarks for GTA: Tokyo, GTA: Bogota as well as the particularly mysterious Grand Theft Auto: Sin City.

Our source added that, as time has gone on, Rockstar has realised the difficulty in moving Grand Theft Auto outside of the USA, where it has firmly embedded itself. There are a number of series staples, from brands to cars, that Rockstar would likely have to change if a future GTA was set somewhere else.

Work on GTA 6 has started

The source also revealed that preliminary work has begun on Grand Theft Auto 6, but said a location had not yet been settled on.

It's not unusual that Rockstar would begin laying the early foundations for its next Grand Theft Auto so soon - It's been more than two years since the initial release of GTA 5.

As for the more immediate future, there's a lot of speculation that next Red Dead game will be revealed this year, but there's a big question over where it could be the first to use a new Rockstar engine. In 2012 Rockstar put out a job advert for a position working on engine development for next-gen systems.

"This is an exciting opportunity to develop cutting-edge architectures and high performance systems for current and next-gen platforms," it read, hinting that a new engine might be in the works. Even if Red Dead Redemption 2 doesn't use it, there's a very good chance that GTA 6 will.

We asked Rockstar for comment on this story but did not receive a reply. We'll update if we hear anything.