A soil sample smuggled out of Syria in a secret British operation appeared to provide the first forensic evidence of chemical weapons being used in the ongoing civil war, The Times of London reported Saturday.

The sample, said to be taken from a neighborhood on the outskirts of Damascus, was delivered to the UK Ministry of Defense’s chemical and biological research establishment at Porton Down in Wiltshire, where it was identified as containing traces of “some kind of chemical weapon.” Though experts could not ascertain which weaponized chemical it was, they did rule out it being tear gas or another crowd dispersal agent.

“There have been some reports that it was just a strong riot-control agent but this is not the case — it’s something else, although it can’t definitively be said to be Sarin nerve agent,” one source told The Times.

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The sample could not indicate whether the use of the chemical was widespread or whether it was fired by forces loyal to President Bashar Assad or rebels.

Opposition activists published a video online last Saturday showing victims on gurneys having trouble breathing or focusing their eyes after an attack on the Jobar neighborhood in the northeast of the capital.

The Times report said the British finding was what spurred Western diplomats to assert on Thursday that the West has firm proof of chemical weapons use.

“In one case, we have hard evidence,” one diplomat was quoted by AFP as saying. And “there are several examples where we are quite sure that shells with chemicals have been used in a very sporadic way.”

Defense sources told the Times that, despite the discovery, there were many unanswered questions. “There has been no Iraq moment,” one source said, referring to the chemical attack by Saddam Hussein against Kurds in Halabja in 1988, which killed about 5,000 people.

Sources said that the evidence, while significant, might not be the “smoking gun” that would give the international community proof that Assad had crossed “the red line” set by US President Barack Obama.

Obama said in 2012 that the use of chemical weapons by the Syrian government would prompt direct action from the United States.

The US, Israel, and Jordan are particularly concerned about the fate of Syria’s stockpile of chemical weapons, which is believed to be divided among several storage sites throughout the country.

In addition to the possibility that Assad may use the weapons as a desperate measure to stay in power, there are fears that some of the weapons may find their way into the hands of terror groups in Syria or Lebanon.

On Monday, UN Secretary-General Ban Ki-Moon urged the Syrian government to accept an expanded UN probe into alleged chemical weapons use, saying he had concluded that an alleged attack in Homs in December warrants investigation.

Syria rejected the expanded investigation, which it had originally sought to look into alleged use of chemical weapons by rebels in March on the village of Khan al-Assal. The rebels blame regime forces.

Britain and France asked the UN to investigate allegations of chemical weapons use in Khan al-Assal and another village, Ataybah, on March 19, as well as Homs on Dec. 23.

The March 19 attack killed 30 and left another 80 injured.

Speaking Tuesday in Rome, Ban said he decided the mission should also look into the Homs allegations and urged Syria to “extend its fullest cooperation and allow the investigation to proceed.”