US Defense Secretary Chuck Hagel said Thursday that the US intelligence community now believes Syria has likely used chemical weapons on a “small scale” against its civilians.

Hagel added that the use of chemical weapons “violates every convention of warfare.”

The statement came on the heels of a public declaration Tuesday by the Israeli army’s top intelligence analyst that forces loyal to President Bashar Assad had used sarin gas against rebel forces and civilians, and may push the US closer to intervening in the two-year-old conflict.

The White House, however, said the news would not necessarily trigger a response.

US Secretary of State John Kerry said the Syrian regime had launched two chemical attacks.

Hagel, speaking to reporters in Abu Dhabi, said the White House had informed two senators by letter that, within the past day, “our intelligence community does assess, with varying degrees of confidence, that the Syrian regime has used chemical weapons on a small scale in Syria, specifically, the chemical agent sarin.”

Britain followed the statement by saying London also believed there had been chemical attacks.

“We have limited but persuasive information from various sources showing chemical weapon use in Syria, including sarin,” a statement by the Foreign Office said. “This is extremely concerning. Use of chemical weapons is a war crime.”

Sarin, used by Saddam Hussein in aerial strikes against Iraqi Kurds in 1988 and in a Japan terror attack in 1995, is a nerve agent that cripples the respiratory system. It is hundreds of times more toxic than cyanide and is considered a weapon of mass destruction.

No information was made public on what quantity of chemical weapons might have been used in Syria, or when or what casualties might have resulted.

A victim of an alleged chemical attack in Jobar, Syria, earlier this month. (Screenshot via YouTube)

A victim of an alleged chemical attack in Jobar, Syria, earlier this month. (Screenshot via YouTube)

Hagel and President Barack Obama have said in the past the use of chemical weapons would be a “game-changer” in the US position on intervening in the Syrian civil war.

However, the White House said the intelligence fell short of what was needed to cross Obama’s “red line” on Syrian chemical weapons.

“We are continuing to do further work to establish a definitive judgment as to whether or not the red line has been crossed and to inform our decision-making about what to do next,” a senior administration official told reporters, according to a report in Foreign Policy. “If we reach a definitive determination that this red line has been crossed, based on credible, corroborated information, what we will be doing is consulting closely with our friends and allies and the international community more broadly, as well as the Syrian opposition, to determine what the best course of action is.”

Alluding to faulty intelligence in the lead up to the 2003 Iraq War, the official said the White House would do its homework before acting.

“I’d say that given our own history with intelligence assessments, including intelligence assessments related to weapons of mass destruction, it’s very important that we are able to establish this with certainty and that we are able to present information that is airtight in a public and credible fashion to underpin all of our decision-making,” the official said.

White House legislative director Miguel Rodriguez, who signed the letter cited by Hagel, wrote that “because the president takes this issue so seriously, we have an obligation to fully investigate any and all evidence of chemical weapons use within Syria.”

The letter went to Sens. John McCain, R-Ariz., and Carl Levin, D-Mich.

The assessment, Rodriguez said, is based in part on “physiological samples.”

He also said the US believes that the use of chemical weapons “originated with the Assad regime.” That is consistent with the Obama administration’s assertion that the Syrian rebels do not have access to the country’s stockpiles.

Reacting to Washington’s announcement, United Nations Secretary-General Ban Ki-moon urged Syria to let inspectors into the country to independently ascertain suspicions that Assad had used chemical weapons.

“The secretary general has consistently urged the Syrian authorities to provide full and unfettered access to the team. He renews this urgent call today,” UN spokesman Martin Nesirky said.

“The fact-finding team is on stand-by and ready to deploy in 24-48 hours,” he added.

Earlier in the week, Hagel and Kerry had said they could not confirm a report by Israeli Brig. Gen. Itai Brun that the IDF was quite certain that Assad deployed chemical weapons against rebel forces in Syria on March 19.

Speaking at a security conference in Tel Aviv on Tuesday, Brun said further that based on the pictures of the victims — the size of their pupils, “and the foam coming out of their mouths” — the army believed that Assad’s troops had used sarin.

Brun also claimed that in Syria today there are over 1,000 tons of chemical weapons, including sarin and VX, both of which can be deployed from artillery rounds and long-range ballistic missiles.

Chemical weapons have been used on more than one occasion in Syria, and the world’s persistent reluctance to act in response to the use of those weapons is typical of the major powers’ current approach to the tremors shaking the Middle East, Brun said.

“We should be very, very worried about [chemical weapons] falling into the hands of those who do not conduct gain-loss considerations,” he said.

Kerry responded to Brun’s comments by saying he had spoken to Israeli prime Minister Benjamin Netanyahu, who could not confirm them.

On Wednesday, Hagel said he had not been briefed on the Israeli assessment during consultations with Israeli Defense Minister Moshe Ya’alon.

He added then that Washington was looking for “real intelligence” on the issue of Syrian chemical weapon use. “Suspicions are one thing. Evidence is another,” Hagel said. “I think we have to be very careful here before we make any conclusions, draw any conclusions, based on real intelligence.”

Times of Israel staff contributed to this report.