It says the dead are a U.S. soldier, an American contractor and five Iraqi workers.  The blast also wounded 20 people, including nine Americans.

Tuesday's attack came as Sunni, Shi'ite and Kurdish leaders continued negotiations to reach agreement on a new Iraqi constitution ahead of a parliament vote on the charter set for Thursday.

Majority Shi'ites and the Kurds are seeking a decentralized government that allows significant regional autonomy.  Sunnis want a centralized government, and warn that a draft constitution defining Iraq as a federal state could be rejected in October's nationwide referendum.

In Washington, U.S. Defense Secretary Donald Rumsfeld stressed that Iraqi leaders must draft a constitution that satisfies Shi'ites, Sunnis and Kurds.