The United Nations Security Council on Thursday gave a green light to an international investigation
aimed at assigning blame for chemical weapon attacks in Syria, the U.N. press office said on Thursday.

The official start of the joint inquiry by the United Nations and the Organization for the Prohibition of Chemical Weapons (OPCW) was delayed due to objections by Russia, which had wanted to expand the investigation to include alleged attacks by Islamic State in neighboring Iraq, diplomats said.

The council’s authorization came in the form of a letter from Russian U.N. Ambassador Vitaly Churkin to U.N. Secretary-General Ban Ki-moon, seen by Reuters.

Ban’s press office confirmed receipt of the letter, saying in a statement that he welcomed it and would, “without delay, undertake all steps, measures and arrangements necessary for the speedy establishment and full functioning” of the inquiry.

Speaking on condition of anonymity, U.N. diplomats said Iraq opposed having the mandate of the Syria investigation broadened to include its territory. Russia had raised other “technical” questions about the inquiry.

The Russian queries, one of which related to the investigation’s financing mechanism, were clarified by Ban in a Sept. 9 letter, which said a trust fund would be established.

Several council diplomats said Moscow was concerned the inquiry could end up confirming allegations by Western nations and rebels that the government of Syrian President Bashar al-Assad has repeatedly used chemical weapons, including deadly sarin and, more recently, chlorine.

Western governments hope the U.N.-OPCW investigation will assign blame to specific individuals that could be used someday to prosecute members of the Syrian government for war crimes.

But prospects for accountability appear remote. Russia and China have blocked for referral of the Syrian conflict to International Criminal Court.

Syria’s government and rebels have denied using chemical weapons.

Western powers say Syria’s government has been responsible for chemical attacks, including chlorine attacks. The Syrian government and Russia, a strong backer of Assad, accuse rebel forces of using poison gas.

Syria agreed to destroy its chemical weapons in 2013 in an effort to avert U.S. military strikes threatened over a sarin gas attack that killed hundreds of civilians. The OPCW has since found chlorine has been “systematically and repeatedly” used as a weapon, though it is not mandated to lay blame.

A separate U.N. investigation had previously determined that sarin gas was used repeatedly in Syria to deadly effect, but that inquiry was also barred from assigning blame.