The Grand Ayatollah Ali Sistani, Iraq's Shiite spiritual leader, has reservations about Iraq's Status of Forces Agreement with the United States, an aide says.

An official from the influential Shiite leader's office said Sistani is concerned with the new agreement between U.S. and Iraqi leaders on the withdrawal of U.S. forces from Iraq, The Washington Post said Saturday.

The international agreement is facing a national referendum sometime before July 30, 2009, leaving voters with the final say.

Under the agreement ratified by the Iraqi Parliament Thursday, all U.S. combat forces will leave Iraqi cities and towns by next summer. That withdrawal will be followed by the removal of all U.S. forces from Iraq by the end of 2011.

The unidentified official said Sistani has not completely rejected the U.S.-Iraq agreement, but rather is urging involved officials to include all Iraqi parties in such diplomatic efforts.

The official told the Post the Shiite leader was also concerned that the wording in parts of the agreement, particularly those regarding the entry and exit from Iraq for U.S. troops, were not clearly specific.