Beirut - Lebanon's president said an investigation into the Beirut port warehouse explosion was looking at whether it was the result of external interference, in addition to simple negligence or an accident, his office said on Friday.
The prime minister and presidency have said 2,750 tonnes of highly explosive ammonium nitrate, which is used in making fertilisers and bombs, had been stored for six years without safety measures at the port warehouse.
It blew up on Tuesday, sending a mushroom cloud and fireball into the sky, killing at least 154 people and smashing a swathe of the city. About 5,000 were also injured.
"The cause has not been determined yet. There is a possibility of external interference through a rocket or bomb or other act," President Michel Aoun said in comments carried by local media and confirmed by his office.
He said he had asked French President Emmanuel Macron, who visited Beirut on Thursday, "to secure aerial images to determine what happened and if the French do not have them, we will request them from another source."
An official source familiar with the initial investigations told Reuters on Wednesday inaction and negligence was to blame for the explosion, after the matter came before several committees and judges and "nothing was done" for years.
The United States said this week it had not ruled out the possibility of an attack, while Israel, which has fought several wars with Lebanon, has been swift to deny any role.
Aoun said the probe would be conducted in three parts: "First, how the explosive material entered and was stored ... second whether the explosion was a result of negligence or an accident ... and third the possibility that there was external interference."
Aoun, who has promised a full investigation, said 20 port officials had been detained as part of the investigation.
The central bank said it froze the accounts of seven individuals, including the port chief and the head of customs.
The source familiar with the initial investigation said a fire had started at port warehouse 9 on Tuesday and spread to warehouse 12, where the ammonium nitrate was stored.
Many Lebanese, who say the government has long sought to blame low-level officials or others for its failings, say the explosion and circumstances surrounding it are symptomatic of political cronyism and rampant graft among the ruling elite, who have presided over the nation as its economy has collapsed.
"Corruption is not only in the port and efforts to fight it must extend to all ports," Aoun said, adding that the investigations would be wide ranging because "the courts are open before the big and the small" officials.