The Lebanese prosecutor probing a port explosion in Beirut in August has filed charges against the caretaker prime minister and three former ministers, Lebanon’s official news agency says.

Judge Fadi Sawwan filed the charges on Thursday against Hassan Diab and former finance minister Ali Hassan Khalil as well as Ghazi Zeiter and Youssef Fenianos, both former ministers of public works.

All four were charged with negligence leading to deaths over the August 4 explosion at Beirut port, which killed more than 200 people and injured thousands.

The explosion was caused by the ignition of a large stockpile of explosive material that had been stored at the port for years, with the knowledge of top security officials and politicians who did nothing about it.

The four are the most senior individuals to be indicted so far in the probe, which is being conducted in secrecy.

About 30 other security officials and port and customs officials have been detained in the probe.