Two years ago, Swedish prog-metal masters Opeth scored an international breakthrough with the release of their fifth album, the epic Blackwater Park (Koch). It was the band’s first disc to be marketed and distributed by the US mega-indie Koch, which has an exclusive licensing deal with their UK label, Music for Nations. For Mikael Akerfeldt, Opeth’s frontman and songwriter, Blackwater Park was a hard act to follow — so much so that he decided to write and record two albums at the same time as an encore.

"I think a lot of people expected us to try and ride the wave of Blackwater Park and just become a commercially successful band without any musical integrity," says Akerfeldt, who called me from Stockholm a few weeks before the start of Opeth’s current North American tour, which hits the Palladium in Worcester this Saturday. "I just felt, I don’t want to paint ourselves into a corner, I want to do something outrageous. I had a plan to do a really heavy album, and I also wanted to use acoustic riffs and mellow arrangements. A friend of mine suggested, ‘Why don’t you do two albums?’ And it just felt like a boost of inspiration to me. I got so into it, I started writing the very same day."

The heavier of the two new Opeth albums, Deliverance, came out in November, but the moody, keyboard-laced Damnation (both Koch) won’t hit stores for another few months. That gives fans plenty of time to sink their teeth into Deliverance, a harrowingly sophisticated work that’s building on the critical buzz of its predecessor: the band combine the technical precision of countrymen Meshuggah and In Flames with a black-metal feel for atmospherics that includes liberal use of percussion and acoustic guitar. Akerfeldt’s voice is uncommonly musical for a death-metal frontman, and his sprawling compositions routinely eclipse the 10-minute mark.

"I grew up listening to the Scorpions and stuff like that, which had some heavy songs and some ballads," he says, explaining his eclectic approach to songwriting. "With Opeth, we just wanted to incorporate both styles into one song. And when I got into the whole symphonic-rock and progressive scene, it added a bit more adventurous feel to the songs. The first symphonic-rock band I heard was Yes, which is a pretty good example of a band that’s doing songs that are more like adventures. Our idea was to do that in an extreme-metal way."

For the most part, Akerfeldt’s lyrics are as unsettling as his music. Take "Deliverance," which doesn’t have the kind of happy ending its title implies. "I based ‘Deliverance’ on this mad guy that had been attacking [guitarist Peter Lindgren]’s girlfriend. He was jealous because his girlfriend had broken up with him, and Peter’s girlfriend was friends with his ex-girlfriend, so she was one of his targets. He had Peter’s girlfriend and a couple of her friends in a room, and he was cutting himself and telling them he would kill them. And he eventually killed himself. Not that the lyric is specifically about his deeds. I just based everything on a madman killer’s point of view."

According to Akerfeldt, the vibe surrounding the recording of Deliverance and Damnation was better suited to the grim nature of the material than he would have liked. Along with his performing and engineering duties, the daunting task of making two albums at once forced him to finish writing in the studio. "It was too much work for me: two months in the studio and half a day off. I was working day and night. When I look back, there’s no good memories about the recording, just black."

He has fonder memories of collaborating with producer Steven Wilson, who fronts the popular UK prog-rock band Porcupine Tree and who first worked with Opeth on Blackwater Park. "Steven acted almost like an additional songwriter, because he came up with some vocal lines and guitar leads. I write all the music in this band, so it feels nice to work with a person that I want to impress to another extent than the guys in the band. Because I know them so well, and they know what I’m going to bring to the table. But with Steven, it’s more intriguing, because he’s such a phenomenal musician and his opinion means so much to me."

As for the band’s rising fortunes in the US, Akerfeldt is happy to share credit with his American label. "Koch pay us tour support, and we’ve been selling so many records in the US, it’s unbelievable. It feels like you’re the fucking king when you come to the US and they take care of you so well. They’re spoiling us."

Opeth perform this Saturday, January 18, at the Palladium in Worcester. Call (508) 797-9696.