President Barack Obama walks after the first day of the G20 Summit on September 5, 2013 in St. Petersburg, Russia. (Igor Russak /Host Photo Agency via Getty Images)

Rep. Alan Grayson, D-Fla., who is aggressively lobbying against a military strike on Syria, says the Obama administration has manipulated intelligence to push its case for U.S. involvement in the country's two-year civil war.

Grayson made the accusation in an interview published Wednesday by The Atlantic and offered more detail in a Thursday discussion with U.S. News. He says members of Congress are being given intelligence briefings without any evidence to support administration claims that Syrian leader Bashar Assad ordered the use of chemical weapons.

Grayson said he cannot discuss the classified briefings, but noted details in the administration's public, non-classified report are being contested.

The White House released its four-page public report Aug. 30, arguing that Assad's government killed 1,429 people on Aug. 21 with a planned chemical weapon attack. Evidence cited in that report included "intercepted communications involving a senior official intimately familiar with the offensive who confirmed that chemical weapons were used."

Grayson, however, says "the claim has been made that that information was completely mischaracterized."

He points to an article published by The Daily Caller that alleges the communications actually showed Syrian officers were surprised by the alleged chemical weapon attack. The communications, according to unnamed sources paraphrased in article, were intercepted by Israeli intelligence and "doctored so that it leads a reader to just the opposite conclusion."

"What they say in The Daily Caller is that [intercepted communications] would lead one to the opposite conclusion," Grayson said. "I don't know if it's right or wrong, [but] there's a very simple way to find out, that's for the administration to show me and other members of Congress" translated transcripts of the intercepts, he said.

Members of Congress are "not being given any of the underlying elements of the intelligence reports," according to Grayson. He's not sure if the information will come before the votes on a proposed strike next week.

The anti-war Democrat said there are other examples of intelligence he believes has been manipulated to favor war.

"Well yes," Grayson said, "but I'm very constrained about talking about it. ... This has become a fundamental problem with our system: The information we do get is limited, but beyond that we are very constrained in discussing it."

Lawmakers are unable to discuss among themselves classified intelligence about Syria unless they are inside an approved reading room beneath the U.S. Capitol Visitor Center and questioning the official account of events, he said, is "actively discouraged."

The four-page White House report on the alleged attack is no more than "a briefing paper with arguments in favor of attacking Syria" that "doesn't present both sides of the issue," Grayson said.

"The administration wants to flood the zone by excluding other information or points of view," he alleged. "I think that it is interesting that the administration consistently refers to Assad doing this and Assad doing that and Assad doing the other thing without giving the public any evidence to support the proposition that Assad has done anything."

White House spokesperson Caitlin Hayden, who fields questions for the National Security Council, chose not to engage Grayson's accusation and directed questions about the veracity of intelligence to federal spy agencies.

The congressman needled administration representatives for more information during a House Foreign Affairs Committee hearing Wednesday. Secretary of Defense Chuck Hagel responded that the Syrian military communications are "probably classified," but that he's unaware of any intentional deception.

The likely outcome for the vote on military action is uncertain in each chamber. Opponents of military action cite intelligence failures before the Iraq War and the fact that many Syrian rebels are al-Qaida-associated religious fanatics who also commit atrocities. A defeat in Congress would embarrass Obama, who stated his intention to strike Syria before caving to pressure and announcing he would seek congressional approval.

"We can't go to war to spare anyone embarrassment," Grayson told U.S. News. "That would be utterly immoral, we're talking about shedding American blood. ... The president has already made that argument and it's falling on deaf ears."

Watch: Grayson grills Hagel: