WASHINGTON (REUTERS, BLOOMBERG) - White House Chief of Staff Mark Meadows said on Wednesday (Aug 5) that the US government has not totally ruled out that a deadly explosion in Beirut, Lebanon, was an attack but said it is still gathering intelligence on the blast the Lebanese government has said was caused by unsafe storage of dangerous chemicals.

"Hopefully it was just a tragic accident and not an act of terror, but we're still looking at all the intel on that," Meadows said in a CNN interview after being asked about President Donald Trump's Tuesday night comments that the explosion was likely a bomb.

Earlier, Defence Secretary Mark Esper, when asked about Tuesday's deadly explosion in Beirut, said that "most believe it was an accident as reported."

He did not elaborate, but Esper's comment on Wednesday to the annual Aspen National Security conference was at odds with Trump's observation the day before that US military officials "seem to think it was an attack. It was a bomb of some kind."

The explosion killed at least 100 people and wounded thousands more.

Authorities blamed a quantity of ammonium nitrate equivalent to 1,800 tonnes of TNT that had been stored at the port, without saying what triggered the blast.

The ammonium nitrate was unloaded from the cargo ship Rhosus in 2014, according to two letters issued by the director-general of Lebanese Customs.

For reasons that are unclear, dockworkers unloaded the chemical, which can be used to make fertilisers and explosives, and put it into storage.

Lebanon is "struggling right now in a number of ways, and it's a shame to see it happen," Esper said.

"When you see the video, it's just devastating."