The Bush administration on Wednesday warned of "real consequences" for Iraq if it rejects a newly negotiated security pact.
Without a deal, the United States could be forced to end its military operations.
The White House said Iraqi security forces are incapable of keeping the peace without U.S. troops, raising the specter of reversals in recent security and political gains if the proposed security deal is not approved by the time the current legal basis for U.S. military operations expires Dec. 31.
"There will be no legal basis for us to continue operating there without that," White House press secretary Dana Perino said. "And the Iraqis know that. And so, we're confident that they'll be able to recognize this. And if they don't, there will be real consequences, if Americans aren't able to operate there."
At the Pentagon, press secretary Geoff Morrell said the U.S. fallback position is to extend the U.N. Security Council mandate authorizing U.S.-led coalition operations in Iraq, but he emphasized that the Bush administration's preference is to complete a bilateral U.S.-Iraqi agreement.
Morrell said Gates has not had direct contacts with Iraqi officials since Baghdad announced this week that Prime Minister Nouri al-Maliki determined that unspecified changes to the draft accord are required. The spokesman said it was not clear what changes the Iraqis are demanding.
The Iraqi government on Wednesday decried statements from Adm. Michael Mullen, chairman of the Joint Chiefs of Staff, who cautioned the Iraqis of unwelcome consequences in the event that the security pact is not signed by the end of the year.
"These statements are not welcomed in Iraq," Iraqi government spokesman Ali al-Dabbagh said in a statement. "All Iraqis realize the volume of their responsibilities and they appreciate the importance of signing the pact or not in the way they deem it proper."
Dabbagh added: "A compulsory method must not be imposed on their choice and it is improper to address Iraqis in such manner."
Morrell said the Iraqis should not take Mullen's comments as an attempt to force anything on them.
"That couldn't be further from the truth," Morrell said. "We are not trying to pressure the Iraqis or force the Iraqis into signing anything they don't wish to sign."