BEIRUT, Lebanon — Britain’s delegation to the chemical weapons watchdog said its director has told a meeting that tests indicate that sarin or a similar toxin was used in an April 4 attack in Syria that killed nearly 90 people.

In a tweet Wednesday, the UK delegation said Ahmet Uzumcu, the director-general of the Organization for the Prohibition of Chemical Weapons, made the statement at the opening of a closed-door meeting of the OPCW’s executive council, which was discussing the attack.

Turkish and British tests also have concluded that sarin or a substance similar to the deadly nerve agent was used.

The United States blamed the chemical attack, on the opposition-held town of Khan Sheikhoun, on the government and fired nearly 60 missiles at a Syrian air base in response.

Syria’s government denies the allegations. The OPCW had no immediate comment.