Search and rescue workers search damaged buildings in Beirut on Thursday, after a huge explosion at the capital city’s port caused widespread damage. Authorities say they have detained 16 people in the inquiry into what went wrong.

Houssam Shbaro/Anadolu Agency via Getty Images

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Houssam Shbaro/Anadolu Agency via Getty Images

Search and rescue workers search damaged buildings in Beirut on Thursday, after a huge explosion at the capital city’s port caused widespread damage. Authorities say they have detained 16 people in the inquiry into what went wrong.

Houssam Shbaro/Anadolu Agency via Getty Images

Authorities in Lebanon have detained 16 people as part of an urgent investigation into the enormous explosion that devastated Beirut’s port area and much of the city on Tuesday. The blast has been traced to an estimated 2,750 tons of ammonium nitrate stored in a warehouse.

Judge Fadi Akiki, a government representative at the military court, said more than 18 people have been questioned so far, including port and customs officials, he said, according to Lebanon’s state news agency.

There are currently 16 people in custody, Akiki said, while others remain under investigation.

The enormous blast killed at least 137 people and injured thousands more. Emergency crews have been working to find all the victims, sifting through rubble and collapsed structures.

French President Emmanuel Macron visited Beirut on Thursday, in a heralded trip in which Macron said he was there to offer support to Lebanon’s people – but not necessarily its government.

“This explosion is the beginning of a new era,” Macron said, describing French disaster aid as a catalyst for political reform.

“Lebanon is in need of change and of a new political contract,” Macron said. He added, “I am not here to support the state or the government; I am here to support the Lebanese people.”

Well-wishers and passers-by seemed the return the sentiment, as crowds of people gathered around Macron when he surveyed the damage in Beirut’s streets. Many in the crowd vented their fury at Lebanon’s leaders.

“Down with the regime!” Beirut residents chanted as Macron’s group moved through the city.

The thousands of damaged buildings includes NPR’s bureau in Beirut. The bureau’s landlord is an architect who has spent his career restoring traditional Lebanese homes, NPR’s Ruth Sherlock says.

“He watched much of his life’s work be destroyed in the blink of an eye,” Sherlock said on Morning Edition Thursday. “And he said, ‘You know, Lebanese are used to damage from the country’s 15 years of civil war. But this destruction was like the destruction of all of the civil war in a single moment.’ “

Ammonium nitrate like the material stored at the warehouse is used for a range of purposes, from making fertilizers to powering bombs. Lebanon’s leaders say the ammonium nitrate had been stored under dangerous conditions for years.

“It seems the ammonium nitrate may actually have come on a ship that made an unscheduled stop at the Beirut port in 2013 because of technical difficulties,” Sherlock says. “And then it was abandoned by the Russian businessman who leased it. Apparently, customs officials appealed six times to Lebanese courts for guidance on what to do,” warning of the risk of keeping a dangerous substance in a crowded city.”

Those details support suspicions that the explosion was not the result of an attack, but simply the result of negligence.