The Lebanese military on Thursday discovered more than four tons of ammonium nitrate near Beirut's port, where a deadly explosion killed nearly 200 people last month.

The military said army experts were called in for an inspection and found the dangerous chemical in four containers near the port. There were no details on the origin of the chemicals or their owner.

The military said customs officials had called in the army to inspect containers at a facility near the port, where they found the ammonium nitrate. It said army experts were "dealing with the material," an apparent reference to it being destroyed.

The port chief, Bassem al-Qaisi, told reporters that there are 43 containers containing flammable material left in the area, adding that the army is doing its best to keep the containers safe. Al-Qaisi said he repeatedly asked customs authorities to take away the material.

Chilean and Lebanese rescuers search in the rubble of a building that was collapsed in last month's massive explosion, after getting signals there may be a survivor under the rubble, in Beirut, Lebanon, Sept. 3. 

Chilean and Lebanese rescuers search in the rubble of a building that was collapsed in last month's massive explosion, after getting signals there may be a survivor under the rubble, in Beirut, Lebanon, Sept. 3.  (AP)

Days after the Aug. 4 blast, French and Italian chemical experts working in the remains of the port identified more than 20 containers carrying dangerous chemicals. The army later said that these containers were moved and stored safely in locations away from the port.

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French experts as well as the FBI have taken part in the investigation into the Aug. 4 blast, at the request of Lebanese authorities. Their findings have yet to be released.

So far, authorities have detained 25 people over last month's explosion, most of them port and customs officials.

The official National News Agency reported Thursday that the lead investigator in the port blast, Fadi Sawwan, heard testimony from the country's caretaker prime minister, Hassan Diab.

Diab, who resigned under pressure following the explosion, is the most senior politician to testify before judicial authorities.

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About 190 people were killed and 6,000 people wre injured in the Aug. 4 explosion that tore through Lebanon’s capital. Investigators said the explosion was caused by about 2,750 tons of ammonium nitrate stacked in unsafe conditions in a port warehouse and neglected for years.

The Associated Press contributed to this report.