Captain America/Steve Rogers (Chris Evans) and Black Widow/Natasha Romanoff (Scarlett Johansson). Picture: Marvel Studios 2018

The 'Avengers: Infinity War' sequel will have "a much bigger role" for both Chris Evans' Captain America and Scarlett Johansson's Black Widow after mainly defending earth during the first of the two movies.

The latest movie in the Marvel Cinematic Universe has been split into two parts, and scriptwriters Christopher Markus and Stephen McFeely have revealed they have always had the second film in mind throughout the project.

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Speaking to the New York Times, the pair admitted that the two characters - played by Chris Evans and Scarlett Johansson - will "have a much bigger role to play in that second film", after mainly being seen defending earth in the first one.

McFeely added: "We gave ourselves license to pay off later."

The duo's comments on the future of the series come after it was suggested Marvel Studios could launch a new Avengers franchise. 

'Avengers 4' - which is scheduled to be released next year - looks set to be the final chapter for the ensemble cast of superhero favourites, but Disney CEO Bob Iger has teased that it might not be the end of an era.

Speaking to The Hollywood Reporter, he said: "We meet on a regular basis with our Marvel team, and we've plotted out Marvel movies that will take us well into the next decade. 

"I'm guessing we will try our hand at what I'll call a new franchise beyond Avengers, but that doesn't necessarily mean you won't see more Avengers down the road. We just haven't made any announcements about that." 

The 67-year-old Disney boss explained that there would be a "significant conclusion" to the storyline - which started in 2008 with 'Iron Man' starring Robert Downey Jr - but he assured fans that it won't be the last they'll see of their much-loved superheroes. 

He revealed: "Given the popularity of the characters and given the popularity of the franchise, I don't think people should conclude there will never be another Avengers movie."