WASHINGTON — President Donald Trump said U.S. military generals have told him that they think the massive explosion that rocked Beirut on Tuesday, killing more than 70 people, was likely a bomb.

“I’ve met with some of our great generals and they just seem to feel that this was not some kind of manufacturing explosion type of an event. … They seem to think it was an attack. It was a bomb of some kind.”

The explosion flattened much of a port and damaged buildings across the capital, sending a giant mushroom cloud into the sky. The death toll, which currently stands at more than 70, and more than 3,000 others were injured, with bodies buried in the rubble, officials said.

The cause of the blast was not immediately known, but initial reports suggested a fire had detonated a warehouse at the port.

Abbas Ibrahim, chief of Lebanese General Security, said it might have been caused by highly explosive material that was confiscated from a ship some time ago and stored at the port. Local television channel LBC said the material was sodium nitrate. Witnesses reported seeing a strange orange-colored cloud like that which appears when toxic nitrogen dioxide gas is released after an explosion involving nitrates.

The explosion came amid ongoing tensions between Israel and the Hezbollah military group on Lebanon’s southern border. Many residents reported hearing planes overhead just before the blast, fueling rumors of an attack, though Israeli military overflights are common. An Israeli government official said Israel “had nothing to do” with the blast. He spoke on condition of anonymity because he was not authorized to discuss the matter with the news media. Israeli officials usually do not comment on “foreign reports.”

U.S. Secretary of State Mike Pompeo extended his “deepest condolences” to the people of Beirut and said the United States is closely monitoring the situation. “Our team in Beirut has reported to me the extensive damage to a city and a people that I hold dear, an additional challenge in a time of already deep crisis,” Pompeo said in a written statement.

The blast was stunning even for a city that has seen civil war, suicide bombings and bombardment by Israel.

“It was a real horror show. I haven’t seen anything like that since the days of the (civil) war,” said Marwan Ramadan, who was about 500 meters (yards) from the port and was knocked off his feet by the force of the explosion.

Emergency teams streamed in from across Lebanon to help, and the injured had to be taken to hospitals outside the capital. Hamad added that hospitals were barely coping and offers of aid were pouring in from Arab states and friends of Lebanon.

Beirut’s governor, Marwan Abboud, broke into tears as he toured the site, exclaiming, “Beirut is a devastated city.” Prime Minister Hassan Diab vowed that “those responsible will pay.”

Initially, video taken by residents showed a fire raging at the port, sending up a giant column of smoke, illuminated by flashes of what appeared to be fireworks. Local TV stations reported that a fireworks warehouse was involved. The fire then appeared to spread to a nearby building, triggering a more massive explosion, sending up a mushroom cloud and generating a shock wave.

One of Israel’s top bomb experts, Boaz Hayoun, said fireworks could have been a factor setting off the bigger blast. “Before the big explosion, … in the center of the fire, you can see sparks, you can hear sounds like popcorn and you can hear whistles,” said Hayoun, owner of the Tamar Group, which works closely with the Israeli government on safety and certification issues involving explosives. “This is very specific behavior of fireworks.”

Charbel Haj, who works at the port, said it started as small explosions like firecrackers. Then, he said, he was thrown off his feet by the huge blast. His clothes were torn.

Some of those injured lay on the ground at the port, Associated Press staff at the scene said. A civil defense official said there were still bodies inside the port, many under debris.

Outside one hospital, Omar Kinno sat on the pavement, holding back tears. Kinno, a Syrian, said one of his sisters was killed when the blast rocked their apartment near the port, and another sister’s neck was broken. His injured mother and father were taken to a hospital but he didn’t know which, and he was making calls trying to track them down.

“I have no idea what happened to my parents. I am totally lost,” he said.

Confusion reigned across the city, as people cleared out of damaged homes or tried to locate family. Motorcyclists picked their way through traffic, carrying the injured.

One woman covered in blood from the waist up walked down a trashed street while talking furiously on her phone. On another street, a woman with a bloodied face looked distraught, staggering through traffic with two friends at her side.

“This country is cursed,” a young man passing by muttered.

The blast came at a time when Lebanon’s economy is facing collapse from the financial crisis and the coronavirus restrictions. Many have lost jobs, while the worth of their savings has evaporated as the currency has plunged in value against the dollar. The result has thrown many into poverty.

Several of Beirut’s hospitals were damaged in the blast. Roum Hospital put out a call for people to bring it spare generators to keep its electricity going as it evacuated patients because of heavy damage.

Outside the St. George University Hospital in Beirut’s Achrafieh neighborhood, people with various injuries arrived in ambulances, in cars and on foot. The explosion had caused major damage inside the building and knocked out the electricity at the hospital. Dozens of injured were being treated on the spot on the street outside, on stretchers and wheelchairs.

“This is a catastrophe we have on our hands,” said one doctor, speaking on condition of anonymity because he was not authorized to make press statements.

The U.N. peacekeeping mission in Lebanon, UNIFIL, said one of its ships in the port was damaged and a number of its peacekeepers were injured, some seriously.

It was reminiscent of massive blasts during Lebanon’s civil war and took place only three days before a U.N.-backed tribunal was set to give its verdict in the killing of former Prime Minister Rafik Hariri in a truck bombing more than 15 years ago. That explosion, with a ton of explosives, was felt kilometers (miles) away, just like Tuesday’s explosion.

French President Emmanuel Macron said in a tweet that his country was sending aid. Israel offered emergency assistance through international intermediaries, its Foreign Ministry said in a statement. Iran, Hezbollah’s patron, also said it was ready to help. “Stay strong, Lebanon,” its foreign minister, Javad Zarif, said in a tweet.

The Associated Press contributed to this report.