Scarlett Johansson has promised that there will be "lots of surprises" in her upcoming Marvel film Black Widow.

The US actress has played the character in the Marvel Cinematic Universe (MCU) since 2010, but this will be the first time she has had a standalone movie focusing on her character.

Johansson introduced Black Widow, also starring Rachel Weisz and David Harbour, on stage at Marvel Studios' Comic-Con panel, as the company revealed phase four of the MCU.

Speaking after the announcement, Johansson said she is "so excited" to reprise the role.

She told PA: "We're going to learn about what haunts this character. You learn a lot about her, there's a lot of surprises.

"It's pretty raw. We go to the brutal, uncomfortable places."

34-year-old Johansson first played Black Widow, a former Russian spy who defected to the Avengers, in 2010's Iron Man 2. "I feel like I've in a lot of ways grown up with this character", she said.

"To be able to come back every two years to this character and peel away layer after layer over this period of time and with this unbelievable fan base, it's kind of incredible."

Rachel Weisz

Meanwhile, her co-star, British actress Rachel Weisz, said the offer to work on the film came "completely out of the blue" from director Cate Shortland.

Oscar-winner Weisz revealed she was so keen to work with the Australian filmmaker that she agreed to play the part before seeing the script.

She said: "She's someone I've wanted to work with for a long time so when I heard it was her, I was kind of blown away. Actually, she works very rarely, she's a real auteur.

"It was incredible, and I hadn't seen the script yet, so that was a very big draw. And Marvel are our contemporary mythology, they're the great storytellers."

Black Widow is due for release on May 1 2020.