President Michel Aoun said some 2,750 tonnes of ammonium nitrate that was stored unsafely in a warehouse caused the blast
The Lebanon government has placed a number of Beirut port officials under house arrest as Tuesday's huge explosion is under investigation.
The blast killed at least 135 people and injured more than 4,000 others. A two-week state of emergency has begun, according to a BBC report.
House arrest would apply for all port officials "who have handled the affairs of storing [the] ammonium nitrate, guarding it and handling its paperwork" since June 2014, Information Minister Manal Abdel Samad said.
The move is an attempt by the government to show the Lebanese people that it is serious about enforcing accountability, the BBC's Arab affairs editor Sebastian Usher says.
But many will dismiss it, as they effectively accuse the entire political elite of culpability through their alleged negligence, incompetence and corruption, our correspondent adds.
President Michel Aoun said some 2,750 tonnes of ammonium nitrate that was stored unsafely in a warehouse caused the blast.
Customs chief Badri Daher said his agency directed to remove the chemical, but "this did not happen".
"We leave it to the experts to determine the reasons," he said.
Ammonium nitrate is used as a fertiliser in agriculture and as an explosive.
Opening an emergency cabinet meeting on Wednesday, President Aoun said: "No words can describe the horror that has hit Beirut last night, turning it into a disaster-stricken city".