By Jonathan S. Landay, Matthew Schofield and Anita Kumar
McClatchy Newspapers
(MCT)

WASHINGTON _ Even as lawmakers pressed President Barack Obama on Thursday to take more aggressive action in Syria, questions surfaced among experts and from within the U.S. government about the strength of the evidence showing that chemical weapons have been used in that nation’s 2-year-old civil war.

White House officials set off a fervor on Capitol Hill when they acknowledged for the first time that the United States had received some evidence that Syrian President Bashar Assad had used chemical weapons, the lethal nerve agent sarin in particular.

Secretary of Defense Chuck Hagel told reporters Thursday in Abu Dhabi that the conclusion had been made in the previous 24 hours.

“We cannot confirm the origin of these weapons, but we do believe that any use of chemical weapons in Syria would very likely have originated with the Assad regime,” he said. “As I’ve said, this is serious business. We need all the facts.”

But experts say the reports should be met with some skepticism because of the small amount of sarin that was found, the lack of widespread deaths and injuries, and inconclusive U.S. intelligence assessments.

The intelligence findings cited in a letter from the White House to Capitol Hill on Thursday were of “low or moderate” confidence, said a U.S. intelligence official who requested anonymity in order to discuss the classified reports.

Another person familiar with the issue, who asked not to be further identified because of its sensitivity, said that only a minuscule trace of a “byproduct” _ a toxic residue left behind after use of a nerve agent, and which he did not identify _ had been found in a soil sample.

“They found trace amounts of a byproduct in soil, but there are also fertilizers that give out the same byproduct,” the person said. “It’s far from conclusive.”

Obama has long resisted significant involvement in Syria, despite repeated calls to help end the bloodshed in the war-torn country. But he has said repeatedly that the use of chemicals weapons would trigger what he called a “red line” and lead to greater intervention.

So far, the United States has provided hundreds of millions of dollars in aid to Syrians seeking to overthrow the Assad regime and has called on the United Nations to investigate the possible use of chemical weapons. That inquiry has been blocked by Assad.

“After two years of brutal conflict, it’s past time for the president to have a robust conversation with the Congress and the American people about how best to bring Assad’s tyranny to an end,” said House Speaker John Boehner, R-Ohio.

Sen. John McCain, R-Ariz., called the disclosure “a game changer.”

Lawmakers of both parties are calling on Obama to provide a safe area for the opposition to operate, to establish a no-fly zone and to offer weapons to the resistance.

“It is clear that we must act to assure the fall of Assad, the defeat of extremist groups, and the rise of democracy,” said Sen. Robert Menendez, D-N.J., chairman of the Senate Foreign Relations Committee. “We must do everything possible to prevent the regime’s use of chemical weapons and to ensure those stockpiles are secure.”

Administration officials said that all options are on the table, but they cautioned that it is too early to judge whether the U.S. should get further involved. Information about the quantity of sarin and the injuries or deaths caused by it were not released, and administration officials raised questions about the chain of custody of physiological evidence.

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(David Lightman and Hannah Allam of the Washington Bureau contributed.)

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