Five years after the September 11 attacks, one of the lingering impacts of that fateful day is the difficulty international artists have in obtaining visas to enter the US.

Massive Attack

Massive Attack, the veteran electronic outfit from Bristol in the UK, were set to kick off their first North American tour in eight years but have had to cancel at least the first four shows of the jaunt because of visa complications.

That means the group won't perform at the Toronto Virgin Festival this weekend as planned, with Broken Social Scene stepping in to fill the void. Muse, the Flaming Lips, the Strokes, Wolfmother, Jose Gonzalez, and the Raconteurs are also set to play the festival.

"We apologize to everyone who bought tickets expecting to see Massive Attack perform," festival organizer Jacob Smid said in a statement. "But we know that the new lineup continues to deliver an outstanding two-day experience." Festival goers who purchased tickets to specifically see Massive Attack can get a refund for their purchases at the point of purchase.

The group, comprised of Robert del Naja (3D) and Grant Marshall (Daddy G) and a slew of vocalists like Cocteau Twins singer Liz Fraser and reggae star Horace Andy, has also canceled shows in Montreal, Detroit, and Chicago because of visa issues.

"In spite of timely and coordinated efforts, the essential US immigration visas were not issued in time for the beginning of the Massive Attack North American Tour," the band said in a statement. "Currently, the rest of the tour remains intact. The band hopes to reschedule the canceled shows as soon as possible."

Massive Attack released a two-disc greatest-hits collection, dubbed Collected, in March and is set to release its fifth studio album, Weather Underground, early next year.