WASHINGTON (CBSDC/AP) — A top Syrian official is calling on the Obama administration to “produce the evidence” that the regime of President Bashar Assad used chemical weapons against its own people.

According to CBS News, Syrian Foreign Minister Walid Muallem said during a news conference in Damascus Tuesday that the case to launch an attack against Syria is “weak and inaccurate” because evidence does not show which side was responsible for the Aug. 21 chemical attack that activists say killed up to 1,300 people.

RELATED: Kerry: ‘Undeniable’ Syrian Regime Used Chemical Weapons Against Own People

Muallem called Secretary of State John Kerry’s claims that it was “undeniable” that the Assad regime carried out a chemical weapons attack “completely wrong.”

Kerry said Monday that the attack should “shock the conscience of the world.”

“It defies any code of morality. Let me be clear: The indiscriminate slaughter of civilians, the killing of women and children and innocent bystanders by chemical weapons is a moral obscenity,” Kerry said in the State Department briefing room.

Secretary of Defense Chuck Hagel revealed Tuesday the U.S. military is ready to strike Syria once President Barack Obama gives the order.

“We are prepared. We have moved assets in place to be able to fulfill and comply with whatever option the president wishes to take,” Hagel said.

CBS News reports that Obama has ordered up legal justifications for strikes against Syria following last week’s chemical attack. A declassified report is expected to be released to the public in the next few days.

Reuters reports that Western powers have told Syrian rebels to expect a strike against Assad’s forces within days.

“The opposition was told in clear terms that action to deter further use of chemical weapons by the Assad regime could come as early as in the next few days, and that they should still prepare for peace talks at Geneva,” a source who attended a Monday meeting between envoys and the Syrian National Coalition in Istanbul told Reuters.

NBC News reports the strike could come as soon as Thursday and would last three days.