ABU DHABI, United Arab Emirates, April 25, 2013 – The U.S. intelligence community assesses with varying degrees of confidence that the Syrian regime has used chemical weapons — specifically the nerve-agent sarin — on a small scale in that violence-torn nation, Defense Secretary Chuck Hagel said here tonight.

On the last evening of his five-nation inaugural trip to the Middle East as defense secretary, Hagel told reporters traveling with him that the White House delivered a letter on the topic this morning to several members of Congress.

“The intelligence community has been assessing information for some time on this issue, and the decision to reach this conclusion was made within the past 24 hours,” the secretary said. “I have been in close contact with senior officials in Washington since then to discuss this serious matter.”

Hagel said the United States can’t confirm the weapons’ origin, but “we do believe that any use of chemical weapons in Syria would very likely have originated with the [Bashar] Assad regime.”

The White House letter, signed by Miguel Rodriguez, director of the Office of Legislative Affairs, on President Barack Obama’s behalf, responded to an April 24 inquiry by unidentified members of Congress. They asked, “Has the Assad regime, or Syrian elements associated with or supported by the Assad regime used chemical weapons in Syria since the current conflict began in March 2011?”

In response, the letter said, “our intelligence committee does assess with varying degrees of confidence that the Syrian regime has used chemical weapons on a small scale in Syria, specially the chemical agent sarin. This assessment is based in part on physiological samples.”

According to the letter, though, the chain of custody is not clear, so it’s not clear how the exposure occurred or under what conditions.

“We need to know the full story and get it right,” Hagel told reporters.

“Thus far,” according to the letter, “we believe that the Assad regime maintains custody of these weapons and has demonstrated a willingness to escalate its horrific use of violence against the Syrian people.”

The Obama administration will remain in close consultation with you and the Congress on these matters, the letter continued. “In the interim, the administration is prepared for all contingencies so that we can respond appropriately to any confirmed use of chemical weapons, consistent with our national interests.”

“As the letter states,” Hagel said, “the president has made it clear that the use of chemical weapons or the transfer of such weapons to terrorist groups would be unacceptable.”

The United States has an obligation to fully investigate, including with key partners and allies and through the United Nations, evidence of chemical weapons use in Syria, the secretary added.

Over the past week, Hagel has traveled to Israel, Jordan, Saudi Arabia, Egypt and the United Arab Emirates, and the military and government leaders of each country have expressed concern about the deteriorating situation in Syria, he observed.

“This subject, Syria, and in particular chemical weapons, is just part of a larger challenge in the Middle East,” Hagel said.

“It is so vitally important for our United States interests, as well as for our allies, that we work … to stabilize and secure these [Middle East] countries,” the secretary concluded, “because if this region of the world essentially gets itself into a situation where it’s ungovernable and out of control, then this will be an astoundingly huge problem for all of the world.”