Rare appearance by Abba foursome 

All four members of supergroup ABBA appeared together at the Swedish premiere of the film Mamma Mia!, delighting fans with their first public showing for years.

Benny Andersson, Bjorn Ulvaeus, Anni-Frid Lyngstad - known as Frida - and Agnetha Faltskog walked down the red carpet at a Stockholm movie theatre to the cheers of several thousand fans.

The movie follows Mamma Mia! the musical, which toured worldwide and features 22 ABBA songs, including Dancing Queen, Take a Chance on Me and The Winner Takes It All.

The foursome, who shot to fame when they won the 1974 Eurovision Song Contest, last performed together in public in 1986, although there were reports they sang together at a private birthday party for a friend in 1999.

They were once reported to have been offered $1 billion to reunite for a concert tour.

At the film premiere, Agnetha and Frida embraced with actress Meryl Streep, posing for pictures before the three did a dance together. Moments later, all four band members appeared on the theatre balcony.

They stood together with Streep, Pierce Brosnan, Colin Firth and other members of the Mamma Mia! cast.

At news conferences, Streep, Brosnan and Firth enthused about ABBA's music while discussing the challenges of singing and wearing figure-hugging Spandex costumes for their roles.

"Once I started singing I kind of rather enjoyed it," Brosnan, better known for James Bond films than musicals, said.

"The Spandex was a bit of a challenge and the boots were. But I had the time of my life making this movie."

Co-star Firth, star of two Bridget Jones's Diary films, said the most frightening aspects of the film were also the most motivating.

"There's an old Miles Davis quote which I've always cherished, which is 'Don't play what you know, play what you don't know'," Firth said.

Ulvaeus had high praise for the actors' vocal abilities. "Most of them don't think they can sing, but they can, I assure you."

The Spandex outfits were a different matter.

"You're going to get bulges that you didn't want and not really developments you did want," said Firth, who performed as Mr. Darcy in the BBC mini-series of Pride and Prejudice.

Streep said she had been excited by the prospect of singing since she had performed in high school musicals such as Oklahoma!.

"That was my beginning so it was kind of like coming home to the thing that I loved very, very much," she said.

Asked to name her favourite ABBA song, Streep said: "I couldn't say. I honestly don't have a favourite song. It's like saying which of your children is your favourite, which of your movies is your favourite. I don't think of it in sports terms like that."