Several helicopters heard flying over Baghdad

Several helicopters could be heard flying over Baghdad on Sunday night, and a letter from the U.S.-led coalition to the Iraqi military seen by Reuters said it would be using helicopters to reposition its troops.

"During this time, there will be an increase in helicopter travel in and around the International Zone (IZ) of Baghdad," the letter, in which the coalition told the Iraqi military it was withdrawing, said.

An Iraqi military source told Reuters the letter was authentic. In Washington, a Pentagon spokesman said he could not immediately confirm its authenticity.