The White House late on November 1 called on Russia to stop blocking efforts to renew the authority of a UN investigative body charged with determining who is behind chemical weapons attacks in Syria.

But the Kremlin on November 2 rejected the U.S. calls, with Russian Deputy Foreign Minister Sergei Ryabkov saying “urgent and drastic measures must be taken to protect” the United Nations’ body “and all activities along this track from U.S. diktat.”

Russia’s Foreign Ministry later issued a statement saying that Foreign Minister Sergei Lavrov told U.S. Secretary of State Rex Tillerson by phone that it is unacceptable to politicize the work of chemical weapons inspectors in Syria.

Authority for the Joint Investigative Mechanism (JIM) of the UN and the Organization for the Prohibition of Chemical Weapons is due to expire on November 17.

At the UN Security Council last week, Russia vetoed a renewal effort led by the United States that would have prolonged the JIM mandate until November 2018.

The UN investigative team last week raised Russia's ire by finding that the Syrian government was responsible for an April sarin gas attack on the Syrian town of Khan Sheikhoun which killed dozens of people. Russia and Syria have denied the allegation.

"This unconscionable attack marks the fourth time that the JIM has confirmed that [Syrian President Bashar al-Assad's] regime used chemical weapons, underscoring the brutal and horrifying barbarism of Bashar al-Assad and making the protection provided by Russia even more egregious," the White House said in a statement.

"Russia’s attempts to undermine and eliminate the JIM show a callous disregard for the suffering and loss of life caused by the use of chemical weapons, and an utter lack of respect for international norms," it said.

"The United States implores the UN Security Council to renew the mandate of the JIM so that we may continue to identify the perpetrators of these horrific attacks and send a clear message that the use of chemical weapons will not be tolerated," the White House said.

The Assad government has repeatedly denied using chemical weapons. It said its air strikes in Khan Sheikhoun hit a weapons depot belonging to rebel forces, a claim “excluded” by the UN's Commission of Inquiry on Syria chairman Paulo Pinheiro.

In vetoing the investigative team's renewal last week, Ryabkov cast doubt on its conclusion that Syria was behind the Khan Sheikhoun attack, saying the investigation involved "dubious witnesses and unconfirmed evidence," according to Russian news agency Interfax.

Russia earlier set out why it disputed UN and Western accusations that the Syrian government had been behind a deadly chemical attack on the opposition-held town of Khan Sheikhoun in April that killed dozens.

The Khan Sheikhoun attack prompted U.S. President Donald Trump to launch missile strikes on Syria's air base in Shayrat, which Western governments say was used to launch the gas attack.

After years of arguing over who is behind frequently reported chemical attacks in Syria, the UN council unanimously agreed to create the JIM in 2015. Its authority was renewed for another year in 2016.

With reporting by Reuters, dpa, and TASS