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By Catherine Chomiak and M. Alex Johnson, NBC News

Secretary of State John Kerry on Monday accused Syria of using chemical weapons against its people, and U.S. officials told NBC News that they would release intelligence evidence to prepare the public for a possible military response.

President Barack Obama hasn't made any decision on whether wage strikes against the regime of Syrian President Bashar Assad, White House press secretary Jay Carney told reporters Monday. But other U.S. officials told NBC News that the administration could begin laying the groundwork by disclosing the evidence as early as Tuesday.

The officials said an attack isn't imminent, because it will take time to make all the information public, and preparations must be coordinated with allies including Britain, France and Turkey. The U.S. is also unlikely to attack while a U.N. weapons team remains in Syria — and it isn't scheduled to leave until Sunday.

The officials reiterated that any military action would be limited and not targeted at Assad because its goal would be to respond to the use of chemical weapons. Targets would be command and control bunkers, airfields and artillery.

Kerry used unusually forceful language in a brief statement to reporters Monday, saying images that have emerged from Syria in the past week — of entire families' being killed without shedding a drop of blood, of bodies' contorting in spasms — "shock the conscience of the world."

He said the evidence was "undeniable" that the Syrian regime had used chemical agents. And he said Obama feels there must be accountability for those who use "the world's most heinous weapons."

Kerry spoke hours after the U.N. team trying to look into claims of a poison gas attack in a Syrian suburb was turned back by sniper fire. At the podium in Washington, Kerry spoke in pained personal terms, as a father, of watching and rewatching video of the aftermath of chemical attacks.

"Our sense of basic humanity is offended not only by this cowardly crime but also by the cynical attempt to cover it up," he said.

As he has frequently since the reported chemical attacks began, Kerry made calls to the foreign ministers of several countries in the region, including Jordan and Saudi Arabia, and to secretary-general of the Arab League.

UN demands protection

The U.N. team, trying to get to a Syrian suburb held by rebels, was first turned back by snipers but later collected blood samples and interviewed survivors. Secretary-General Ban Ki-moon, saying the six-car convoy had been "deliberately" targeted, demanded that the regime and opposition forces ensure "the safety and security of the investigation teams."

"Despite such very difficult circumstances, our team returned to Damascus and replaced their car and proceeded to a suburb of Damascus to carry on their investigation," he said. "They visited two hospitals. They interviewed witnesses, survivors and doctors. They also collected some samples."

The investigation centers on a rebel-held suburb of Damascus known as Eastern Ghouta, where activists say rockets loaded with poison gas killed hundreds of civilians Wednesday, many of them women and children.

Reuters cited residents saying at least one mortar bomb fell in the area near the Four Seasons hotel, where the U.N. officials are staying. State media said the bombs had been fired by "terrorists," the term it uses for rebels fighting Assad.

The U.S. postponed a meeting with a Russian delegation scheduled for this week at the Hague to discuss an international peace conference for Syria, a senior State Department official told NBC News Monday night. "Given our ongoing consultations about the appropriate response to the chemical weapons attack in Syria on Aug. 21, we have decided to postpone," the official said, adding: that "we will work with our Russian counterparts to reschedule" and "it is imperative that we reach a comprehensive and durable political solution to the crisis in Syria."

Support builds in Congress

The administration has won some preliminary support for a military response from members of Congress, but lawmakers differed over the scope of a possible attack and bickered over how much consultation they're being allowed with the White House.

"I do think action is going to occur," Sen. Bob Corker of Tennessee, the top Republican on the Foreign Relations Committee, said on TODAY.

A Democrat, Sen. Bob Casey of Pennsylvania, backed also limited military involvement.

"Taking action now will certainly be more difficult than it was last year, but if the administration does decide to act in collaboration with our allies in Europe and the Middle East, it should act decisively to avoid further extending the conflict," Casey said.

Republicans in the House, however, demanded that Obama keep them informed of any plans to wage strikes against Syria — suggesting by implication that the administration hadn't yet done so to the party's satisfaction.

Brendan Buck, a spokesman for Speaker John Boehner, R-Ohio, said Boehner "had preliminary communication with the White House about the situation in Syria and any potential U.S. response" Monday afternoon.

"The speaker made clear that before any action is taken there must be meaningful consultation with members of Congress, as well as clearly defined objectives and a broader strategy to achieve stability," Buck said.

Earlier Monday, before news of the discussion emerged, Buck was more emphatic, saying: "The president is the commander-in-chief, but the first step is for him and his team to consult with Congress on what he considers viable options. That has not yet taken place."

Carney, however, insisted that "we're consulting with Congress and will continue to do that."

Meanwhile, in an interview with a Russian newspaper, Assad denied that his forces had used chemical weapons and predicted that any U.S. military intervention in his country would be unsuccessful.

"Failure awaits the United States as in all previous wars it has unleashed, starting with Vietnam and up to the present day," he told the pro-Kremlin newspaper Izvestia. "Would any state use chemical or any other weapons of mass destruction in a place where its own forces are concentrated? That would go against elementary logic."

Russia also criticized the tough talk, urging the U.S. not to "repeat past mistakes."

Foreign Minister Sergei Lavrov said at a Moscow news conference that no evidence had yet been produced about the use of chemical weapons in Syria and that military action without U.N. Security Council approval would be "a very grave violation of international law."

Marie Harf, a spokeswoman for the State Department, dismissed contentions like that, telling reporters: "Anybody who thinks that this could be manipulated evidence, that these videos could be doctored somehow, needs to check their conscience, because it's ridiculous."

Ammar Cheikhomar, Alastair Jamieson, Albina Kovalyova, Andrea Mitchell, Ayman Mohyeldin, Michael O'Brien and Erin McClam of NBC News contributed to this report.