Russia used its U.N. veto Tuesday to block a resolution extending the mandate of the investigators probing chemical weapons attacks in Syria.

In a Security Council vote, 11 countries supported extending the mission for another year, while Russia and Bolivia voted against the measure, and China and Kazakhstan abstained.

The investigating team, known as the Joint Investigative Mechanism or JIM, is expected to make public a report on Thursday that could identify the party responsible for a deadly April 4 attack in the rebel-controlled town of Khan Sheikhoun in southern Idlib that killed and sickened scores of civilians.

Three days later, the United States launched an airstrike on a Syrian air base which Washington accused the regime of Bashar al-Assad of having used to launch the poison gas attack.

Accountability

While the question of whether sarin or a sarin-like substance is not disputed, who used it still has to be officially confirmed, and it is anticipated the JIM’s report could shed light on the matter.

It would be politically embarrassing for Russia, a staunch ally of President Assad, if evidence shows that the regime — and not, for example, Islamic State militants — are responsible for the attack. In Syria, the government is the only party to the conflict that possesses air capabilities. Russia has previously suggested that the gas was released from a bomb on the ground and not in the air.

Russia’s U.N. envoy, Vassily Nebenzia, first sought to postpone Tuesday’s vote through a procedural measure until after the release of the JIM’s report, saying the hastily-called vote was an effort by Washington to embarrass Moscow.

“You need to show up Russia and show that Russia is guilty of not extending the JIM, in fact you are the one who is begging for confrontation,” Nebenzia said of the U.S. delegation, which drafted the text and pushed for the vote.

While the procedural vote had the support of China, Kazakhstan and Bolivia, it fell short of the required eight-vote majority and failed to prevent the other vote going ahead, forcing Russia to use its veto.

Eighth veto on Syria

“I want to underscore that today’s voting is senseless also, because it won’t have any impact on the future of the JIM,” Nebenzia said after casting his veto — the eighth time Russia has done so on Syria. “We will return to the issue of extension in the future — we have not stopped it.”

The mission’s mandate does not expire until November 16, so the council has three weeks to approve an extension without disrupting the team’s work, as happened last year when consensus could not be reached on the JIM’s extension.

“The question we must ask ourselves is, whether the JIM is being attacked because it has failed in its job to determine the truth in Syria, or because its conclusions have been politically inconvenient for some council members,” said U.S. envoy Michele Sison.

“Russia called for the formation of the JIM, they negotiated its terms, they agreed its mission, and yet when faced with the prospect of the JIM revealing the truth, why has Russia alone chosen to shoot the messenger?” asked British Ambassador Matthew Rycroft.

Some diplomats said the move for the vote now was intended to avoid politicizing whatever conclusions the report draws and avoiding having them affect votes for the extension.

All council members expressed the hope that they could return to the issue and reach consensus on extending the JIM’s mandate before it expires next month.