WASHINGTON – The United States Wednesday raised the prospect that Syria will miss the first test of its compliance with an agreement to give up its chemical weapons.

While Secretary of State John Kerry has said that Syria “must submit” a full disclosure of its chemical weapons by Sept. 21, as called for in the U.S.-Russia accord, State Department spokeswoman Marie Harf said Wednesday that the U.S. was prepared for some delay. She said the date — one week after the accord was reached in Geneva that averted U.S. military strikes — was more a “timeline” than “a hard and fast deadline.”

The comments may indicate that the U.S. anticipates Syrian President Bashar Assad is unwilling or unable to meet the first goal set out in the agreement and that the U.S. doesn’t want that date to become a make-or-break condition. Harf told reporters in Washington that what counts is seeing “forward momentum, understanding that it’s complicated and that these are targets on a calendar.”

The accord negotiated by Kerry and Russian Foreign Minister Sergei Lavrov says their countries “expect Syria to submit, within a week, a comprehensive listing, including names, types, and quantities of its chemical weapons agents, types of munitions, and location and form of storage, production, and research and development facilities.”

Kerry was more emphatic at a Sept. 14 news conference with Lavrov in Geneva, where he said “we agreed that Syria must submit, within a week — not in 30 days, but in one week — a comprehensive listing.”

Members of Congress briefed by Kerry this week also said they got the impression that the Sept. 21 date was more than just an aspiration.

“We’re hopeful that these deadlines will be met,” Sen. Dick Durbin, D-Ill., said after Kerry discussed the accord with the Senate Foreign Relations Committee. “And we’re going to hold the Syrians to them.”

Syria on Wednesday gave Russia what it said was additional evidence supporting its case that rebels, not the regime, were responsible for a Aug. 21 chemical weapons attack near Damascus.

Russian Deputy Foreign Minister Sergei Ryabkov said during a visit to Damascus that Russia is “unhappy” about the findings of a U.N. investigation, according to Russian state broadcaster RT. While the U.N. didn’t say who was to blame for the attack, Western nations and human-rights groups said the evidence it provided made clear the Assad regime was behind it.

“We think that report was distorted, it was one-sided, the basis of information upon which it is built is not sufficient, and in any case we would need to learn and know more on what happened beyond and above that incident of Aug. 21,” Ryabkov told RT.

Lavrov called Tuesday for further inquiry, saying his country has “serious grounds” for thinking that the attack last month was a rebel “provocation,” as Assad claims.