"We are very disappointed to have to postpone our U.S. engagements," said the agency's Cezary Szyjko in a statement. "However, once these issues are resolved we look forward to bringing the Alexandrov Chrous to the United States."

A representative of Heinz Hall in Pittsburgh said she had not been aware of any visa problems, and said the group's planned performance there had suffered from slower-than-anticipated ticket sales. She added that she expected the group to schedule a new date in spring 2005.

Performances in Minneapolis, Washington, and Detroit were also affected.

The group, celebrating its 80th anniversary, was to perform a program of folk songs, liturgical music, and Soviet-era military songs. The tour would have been its first in the United States since 1989.