Russia blocked an effort to extend an investigation into Syria's use of chemical weapons, by casting a veto Tuesday at the United Nations Security Council.

The investigation into chemical weapons in Syria has been a political football for years, but especially in recent months following President Trump's authorization of an airstrike against Syrian President Bashar Assad's regime in April. But Russian President Vladimir Putin has argued that Assad might have been framed by terrorists in order to justify the strike, a claim that set the tone for the debate over the UN's Joint Investigate Mechanism, of JIM, for reviewing the attacks.

"We reject this cynicism, and we reaffirm our confidence in these technical experts, men and women who come from many regions, many backgrounds, and many perspectives," U.S. Ambassador Michele Sison, the deputy representative at the United Nations, told the Security Council on Tuesday about Russia's position. "They knew their work would be attacked by Syria's allies, yet have carried out their mandate effectively and responsibly."

The UN's investigatory body is set to expire in November, but it has not yet issued its final report on the Syrian attacks. Russia cited the lack of that report as a reason not to extend the JIM's mandate.

"To make sure the UN Security Council's decision on this issue is grounded in fact, it is first necessary to read the report because the UN Security Council did not receive any meaningful information on the JIM's activities this year," the Russian Foreign Ministry said in a Monday bulletin. "There was no report but there was a demand to extend the mandate. This won't do."

British diplomats scoffed at that reasoning. "The whole point of going now, with this vote, in advance of the next report, is to keep the politics out of this decision, and to make it a technical rollover of what is a professional, independent, objective and highly regarded body," Matthew Rycroft, the UK ambassador to the UN, told reporters Tuesday.

Russia's veto of the extension was presaged by criticisms of an earlier UN report on the controversy, culminating in an aggressive reading of a State Department travel warning for Syria. The Russia Defense Ministry cited language in the warning that acknowledged the use of chemical weapons but blamed it on terrorist groups.

"This is the first official recognition by the State Department not only of the presence, but the very use of chemical weapons by Al-Nusra terrorists to carry out terrorist attacks, which we repeatedly warned about," said General Igor Konashenkov, according to state media.

The State Department maintained that the warning only referred to the American assessment that the Islamic State in Syria has used chemical weapons. "Their comments are a deliberate attempt to yet again deflect from the documented fact that the Assad regime has committed multiple chemical weapons attacks against its own people," Edgar Vasquez, a State Department spokesman, told the Washington Examiner in an emailed statement.

Western diplomats continued with that line of criticism Tuesday. When Russia accused the UN investigators of failing to collect soil samples that would help establish whether Assad was involved in the attack, the American representative reminded the security council that the Assad regime provided soil samples that tested positive for chemical weapons.

"We want to know the truth about these attacks, regardless of where it takes us," Sison said. "The United States deeply regrets that one member of this Council vetoed against this text, putting political considerations over the misery of Syrian civilians who have suffered and died from the use of chemical weapons. The reasons offered fool no one this morning."