Scarlett Johansson's Black Widow will play a ''very big'' part in 'Avengers: Age of Ultron'.

The 29-year-old actress is to reprise her role as the Black Widow, Natasha Romanoff in the upcoming superhero sequel and Marvel's Kevin Feige has revealed she will be integral to the plot.

Explaining that the Black Widow will not be getting her own stand-alone film, Feige said: ''Black Widow couldn't be more important as an Avenger, but, like Hulk, the Avengers films will be the films where they play a primary role.

''Her part in Avengers: Age of Ultron' is very, very big and further develops her character. The plans we have for her through the rest of the Avengers saga are very big and she is a linchpin, in fact, to those films.''

The producer and president of Marvel films insisted that while Black Widow could be the subject of a solo film in the future, they're focusing on her place in the 'Avengers' films for the foreseeable future.

He added: ''So instead of taking her out there or doing a prequel which we haven't done yet, we're continuing the forward momentum of the continuity of the Cinematic Universe, of which Widow is a key part.''

'Age of Ultron' is the follow up to 2012 film 'The Avengers' and will also see the return of characters including Iron Man (Robert Downey Jr.), Thor (Chris Hemsworth) and Captain America (Chris Evans) when it's released in April next year.

Meanwhile, Marvel has also announced they are planning a further two-part 'Avengers' story titled 'Infinity War', which will be released in 2018 and 2019.