Russia on Thursday vetoed a United Nations Security Council resolution to extend an international inquiry to find out who was behind the chemical attacks in Syria’s Khan Sheikhun on April 4. More than 100 civilians were killed in the sarin gas strike, allegedly carried out by the Bashar al-Assad government.

The UN and the Organization for the Prohibition of Chemical Weapons have been investigating the sarin gas attack, but their mandate expired at midnight on Thursday. Without Russia’s vote, the investigation cannot go ahead for now.

US Ambassador Nikki Haley and French Ambassador François Delattre criticised Russia’s veto, CNN reported. Haley called it a “deep blow” to UN efforts to identify those using chemical weapons, and Delattre said, “It promises great difficulties for the future.”

To be adopted, a resolution needs nine votes in its favour and no vetoes by the US, China, Russia, France or Britain – the permanent members of the UN Security Council. With this vote, Russia has vetoed 10 UN resolutions on Syria since the conflict began in 2011. It had also vetoed a US bid on October 24 to renew the Joint Investigative Mechanism for inquiry into the use of chemical weapons in Syria.

Russia has repeatedly questioned the findings of the team. In October, the investigators said Syria’s ruling regime under Bashar al-Assad was responsible for the deadly attack.