UNITED NATIONS (AP) — Britain's U.N. ambassador called Friday for sanctions against Syria after international chemical weapons investigators declared the Syrian government responsible for a sarin nerve gas attack that killed over 90 people last spring.

But it's not clear what action, if any, would pass muster with veto-wielding Syrian ally Russia, which dismissed the experts' findings as inconsistent and unpersuasive. And while the British envoy said the Security Council needs to "impose accountability," his French counterpart focused on finding common ground on an issue that has spurred a series of Russian vetoes.

The attack in the Syrian town of Khan Sheikhoun in April sparked outrage around the world and a U.S. strike days later on the Shayrat air base, where Washington said the attack had been launched. Syria's government has denied involvement.

But the investigators' new report, obtained Thursday by The Associated Press, says experts are "confident" Damascus was behind the sarin strike, based on photos, videos and satellite images as well as studies of munition remnants. The report was done by what's known as the Joint Investigative Mechanism, or JIM, which the United Nations and the Organization for the Prohibition of Chemical Weapons established to determine responsibility for chemical attacks in Syria.

The report also blamed the Islamic State extremist group for a September mustard gas attack in Um Hosh in Aleppo.

In light of the findings, British Ambassador Matthew Rycroft said Friday that the Security Council needs to follow through on a 2013 vow to respond to any chemical attacks in Syria with use of a U.N. charter chapter that generally amounts to sanctions.

"It now falls on the Security Council to act on these findings and to deliver justice," he said, exhorting Russian officials "to find their moral compass and join the Security Council in following up this use of sarin by the regime and making sure, once and for all, that all those responsible are held to account."

Britain, France and the United States spearheaded an effort last winter to ban helicopter sales to Syria and impose an asset freeze and travel ban on 11 Syrian military officers and others over prior chemical attacks; Russia and China vetoed that measure. U.S. Ambassador Nikki Haley, who was traveling in Africa on Friday, said in response to the new report that the council should make it clear that chemical weapons use by anyone "will not be tolerated."

French Ambassador Francois Delattre vowed accountability for those responsible for the Khan Sheikhoun attack. As for whether that means a sanctions effort, he said discussions were ongoing, but "the key priority now is to recreate consensus."

The report came days after Russia vetoed a proposal to extend the JIM's work, with Ambassador Vassily Nebenzia saying that the matter should wait for the findings and that Moscow will insist on amending the group's mandate to ensure "the professionalism and impartiality that we want to see."

Russia has questioned the JIM's methods, and Moscow has said its own analysis of photos of the Khan Sheikhoun attack site suggest that what happened was not an airstrike, but an explosion on the ground.

Russia's Foreign Ministry said Friday that the JIM had ignored Moscow's input.

"The report includes completely contradictory conclusions" that "are not supported by any convincing argument," the ministry said in a statement.

___

Associated Press writer Jim Heintz contributed from Moscow.