Report: Syria may miss first deadline of chemical weapons deal

At the time, Kerry said the United States would not accept "anything less than full compliance."

But on Wednesday, State Department spokesperson Marie Harf said that the U.S. did not "want to put a hard and fast deadline on it."

"Our goal is to see forward momentum, and obviously we know it takes time as well.  This is really the first step in assessing how serious the Syrian regime is at working towards this framework that us and the Russians have agreed to," Harf said. "Obviously, if they submitted a list that was less than complete or that we thought was less than complete, we’ll address that then."

The State Department said that it was unclear whether the Assad regime had available a centralized list of its chemical weapons holdings, and conceded the deadline could slip.

But Harf said the goal was obtaining a "comprehensive" declaration as "swiftly as possible" without "setting arbitrary deadlines."

"It’s going to be a complicated process with ups and downs," she said. "Nobody’s naive about that. We’ll keep working with the Russians.  But let’s be clear that the onus here is on the Syrian regime to live up to their obligations."

Critics of the White House have warned that the deal to turn over Syria's chemical weapons could be a stalling technique by the Assad regime and its allies in Moscow. On Sunday, Sen. John McCain (R-Ariz.) told "Meet the Press" that there was "not a seriousness on the part of the Russians."

In an interview with Fox News that aired Wednesday, Assad himself admitted publicly for the first time that his country had chemical weapons.

"It's not a secret anymore," Assad said.