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By Mike Mount and Elise Labott reporting from Chicago

The United States and Pakistan will not reach a deal on opening NATO supply routes before coalition leaders meet on Sunday, two senior U.S. officials told CNN.

"There is no deal, and there won't be one until President (Asif Ali) Zardari returns" to Pakistan, one senior official said, "and even that is not assured."

The two sides had hoped to have a deal before Zardari arrived in Chicago this weekend to join NATO allies and other coalition partners for a meeting on Afghanistan.

"The main thing is to get a deal," one senior official said. "It's less important as to when."

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