AMSTERDAM (Reuters) - A Spanish diplomat has been proposed to head the world’s chemical weapons watchdog at a critical time for the organization’s disarmament work in Syria, diplomats said on Wednesday.

A vote on the appointment of Fernando Arias, 65, is expected to be taken by the 41-member executive council of the Organization for the Prohibition of Chemical Weapons on Thursday.

The change of leadership comes as the OPCW and U.N. weapons inspectors investigate ongoing use of banned nerve agents, including sarin and mustard gas, in the Syrian civil war.

Syrian officials remain unable to explain how banned chemicals have been found in the country, meaning the new leader could face a showdown among members over whether Syria should be reported to the United Nations for non-compliance.

“We believe that we have a strong successor in Ambassador Fernando Arias of Spain, and hope that the executive council will agree his nomination by consensus,” said Ambassador Peter Wilson, head of the British delegation at the OPCW.

Arias will have to overcome fundamental differences between major powers Russia and the United States, which jointly drafted a deal to rid Syria of its chemical weapons in 2013 after a sarin attack killed hundreds of civilians near Damascus, but have since ended cooperation at the OPCW.

The Syrian government has repeatedly denied using chemical weapons during the more than six-year civil war.

But despite a massive international mission to destroy its toxic arsenal, OPCW inspectors have found use of chemical weapons is systematic and ongoing.

Diplomats say Arias, Spain’s ambassador to the OPCW and the Netherlands, where the organization is based, is known as a strong negotiator and mediator, making him a good match for the job.

Under Arias’ direction, the OPCW adopted a contentious decision in 2016 condemning the use of chemical weapons by Syrian government forces and Islamic State militants.

A rare vote at the consensus-based OPCW signaled the break in cooperation between the United States and Russia, which back different sides in the war.

The United States had sought to impose sanctions on those responsible through the OPCW’s executive council, but dropped the proposal in the face of fierce Russian opposition.

An alternative text drafted by Spain was supported by a majority, including Germany, France, the United States and Britain, but opposed by Russia, China, Iran and Sudan.

Arias nomination must be formally be approved by all the OPCW’s member countries, represented through the Conference of States Parties, which is expected by December. He will succeed Ahmet Uzumcu of Turkey, who has headed the since July 2010.

Arias, who previously served as Spain’s ambassador to the United Nations, will be appointed for a four-year term through July 2022 and can seek reappointment.

He was picked over candidates from Denmark, Hungary, Lithuania, South Korea, Burkina Faso and Iraq, diplomatic sources told Reuters on condition of anonymity because the process was confidential.

Born in Madrid, Arias also held positions in Mauritania, Bulgaria, Montenegro and was as deputy ambassador in China.