Grand Ayatollah Ali al-Sistani (file photo)

Iraq's top Shi'ite Muslim cleric has expressed concern about the security pact approved earlier this week allowing U.S. troops to remain in the country for three more years.

A senior aide to Grand Ayatollah Ali al-Sistani said Saturday that the influential cleric fears the deal will not guarantee Iraq's sovereignty. He also said he feels there is no national consensus on it.

The aide said Ayatollah al-Sistani supports holding a referendum on the pact, which lawmakers agreed to do in order to get the approval of the main Sunni faction.

The reclusive cleric does not often get directly involved in politics, but his views carry immense weight in Iraq's large Shi'ite community.

Iraqi lawmakers signed the security pact with the United States earlier this week. It was approved by the main Sunni, Shi'ite and Kurdish factions, but opposed by lawmakers loyal to opposition cleric Moqtada al-Sadr.

The deal is expected to be approved by Iraq's three-member presidential council.  The agreement would replace the U.N. mandate for the U.S. military presence in Iraq.  That mandate expires December 31.

The new security agreement calls for U.S. forces to withdraw from Iraqi cities by June 30, 2009, as an interim step.  It also gives Iraq strict oversight over some 150,000 U.S. forces in the country.

Earlier Saturday, a rocket attack near a U.N. compound in Baghdad's heavily fortified Green Zone killed at least two foreign workers and wounded at least 15 others.

A U.N. statement said the two foreigners killed were working for a catering company. The victims' nationalities were not immediately reported.

The United Nations has had a limited presence in Iraq since a suicide bomber struck the organization's Baghdad headquarters five years ago. The blast killed 22 people, including top U.N. envoy Sergio Viera de Mello.

Some information for this report was provided by AFP, AP and Reuters.