As work on their long-awaited follow-up to 2003's "St. Anger" continues, metal icons Metallica [ tickets ] have rolled out plans for a summer run on the European festival circuit, and will warm up for that trek with a newly added US performance.

"The gears are starting to turn here at HQ and just as we're getting ready for our annual European summer vacation, our friends at radio station KFMA invited us to head over to Tucson, AZ for their big show at the Pima County Fairgrounds on Friday, May 16," the group wrote in a message posted at its website. "We're looking forward to sharing the stage with our friends Apocalyptica, Scars on Broadway, and Flobots."

The Tucson show is one of only two US dates that currently grace the group's schedule; the other is a previously announced June 13 performance at this summer's Bonnaroo festival.

Following the mid-May show in Arizona, the band will jet across the pond to hit a number of Euro festivals, dates for which are scattered through late summer. Details are available at the group's website.

The newest additions to Metallica's festival plans are headlining sets at the Reading and Leeds Festivals in late August.

"This isn't the end of the line for those of you keeping score," the group said in a message posted at its site today (3/31). "We have a few more to come, so to use that tired line again, 'keep watching here.'"

Metallica has been working on its next album with producer Rick Rubin. A release date has not been announced.