Chemical experts and firefighters are working to secure at least 20 potentially dangerous chemical containers at the explosion-shattered port of Beirut, after finding one that was leaking, the Associated Press reports citing a member of a French cleanup team.

Some of the containers were punctured when the deadly blast ripped through the port on August 4 and the Lebanese capital, said Lt. Anthony, a French chemical expert at the site who was not authorized to be identified by his full name according to government policy.

French and Italian chemical experts working amid the remains of the port have so far identified more than 20 containers carrying dangerous chemicals, Anthony said.

“We noted the presence of containers with the chemical danger symbol. And then noted that one of the containers was leaking,” he told The Associated Press in a TV interview on Monday.

The experts are working with Lebanese firefighters to secure all of the containers and analyze their contents, he said. “We need to clean everything and put all in security.”

He didn’t identify what chemicals were involved or provide further details. Lebanese officials have not commented on the potential chemical risks at the port.

The explosion on August 4 in the port killed at least 220 people and injured about 6,000 others. It is believed to have been caused by a fire that ignited a 2,750-ton stockpile of highly volatile ammonium nitrate. The material had been stored at the port since 2013 with few safeguards despite numerous warnings of the danger.