A Lebanese judge has reportedly charged caretaker Prime Minister Hassan Diab and three ex-ministers with negligence over August's Beirut port explosion. Judicial sources said the four would be questioned next week about warnings they received over the unsafe storage of ammonium nitrate in a warehouse. A fire triggered the detonation of 2,750 tonnes of the chemical, causing a massive blast that killed 200 people. Mr Diab said his conscience was clear and expressed surprise at the charges. He and his cabinet resigned days after the explosion, which he blamed on what he called a "system of corruption... bigger than the state". The disaster compounded a deep economic crisis in Lebanon that has led to hundreds of thousands of people taking to the streets to demand the removal of a political elite that they accuse of graft, mismanagement and negligence. There was widespread anger and disbelief that such a large quantity of ammonium nitrate was kept inside a port warehouse without any safety measures, so close to the centre of Beirut. The chemical - which is widely used as agricultural fertiliser but can also be mixed with fuel oil to make explosives - arrived in the capital in 2013 on a Moldovan-flagged cargo ship, the MV Rhosus.