Seoul, South Korea - K-pop megastars BTS released a new album on Friday, as buzz built ahead of their open-air comeback concert in Seoul that will go ahead despite leader RM being advised to rest his injured ankle.

The Saturday gig, expected to draw around 260,000 people, will be BTS's first after a hiatus of almost four years while all seven members served compulsory military service. It comes ahead of an 82-date world tour.

On Friday, BTS's management said that medical staff recommended RM, 31, wear a cast and "minimize all physical movement" for at least two weeks after hurting his ankle the day before in rehearsals.

But "the artist himself expressed a strong desire to deliver a performance of the highest quality," Big Hit Music said.

"Consequently, we wish to inform you that RM's participation in certain performance elements, such as choreography on stage, will be restricted," a statement added.

Earlier, BTS released their fifth studio album, billed as reflecting the maturing boy band's Korean roots and identity.

Streaming giant Spotify said that fans pre-saved the album more than five million times, a record for a K-pop act.

The 14-track ARIRANG takes its name from a folk song about longing and separation that is often dubbed South Korea's unofficial national anthem.

"We gave deep thought to our identity – and how best to express ourselves authentically – across the entirety of our music and performances," said BTS member Jimin, 30.

"As an extension of that process, we also revisited the significance of our background as a group comprised entirely of Korean members," he said in a statement.

Ces-Marie Hilo (40), a fan from the US, said she listened to the album while waiting to purchase BTS merchandise.

"We are still listening to the album, and it's amazing so far," Hilo told AFP. "I can hear tidbits from their roots, but the majority are new sounds from them and a mix of different genres."