Nasa has raised doubts about whether a loud boom and a gaping crater found in Nicaragua this weekend were caused by a meteorite, as the government said.

Nasa said that while a meteorite cannot be ruled out, the lack of any witness accounts of a fireball lighting up the nighttime sky outside the capital suggests another cause. Photos showed a crater about 39ft wide in a wooded area near Managua's international airport.

The head of Nasa's Meteoroid Environment Office, Bill Cooke, estimated it would have been created by a blast of roughly the energy equivalent of 1 tonne of TNT.

Nasa said in a statement that a meteor capable of that would have created a ball of flame visible over a wide area. About 1.5 million people live in Managua.

Cooke said: "For something to produce a hole in the ground that big, it would have generated a very bright fireball. And nothing was reported … despite the population. So I'm very sceptical."

There was no word so far of any meteorite fragments being found in the crater.

Rosario Murillo, a government spokeswoman and wife of the president, Daniel Ortega, said on Sunday that a relatively small meteorite was responsible for the phenomenon. The following afternoon she said scientists from other countries had expressed interest in coming to investigate.

Jaime Incer, a scientist who advises the Nicaraguan presidency on environmental matters, said he could not confirm for sure it was a meteorite, but said that "among the possibilities, it's one of the most likely". He said he suspects a meteorite composed of rock.

Incer said it was possible nobody was looking up at the sky when the event took place late at night. Residents described it as a loud boom.

"I was walking back home after playing billiards, and suddenly I heard the explosion and felt the shockwave, which was very strong," said Victor Gutierrez, a 38-year-old mechanic who lives less than a mile from the site of the crater. "I didn't see anything in the sky either before or after."

Incer and Lindley Johnson, an executive for Nasa's Near-Earth Object Observations Program, agreed that whatever happened in Nicaragua had nothing to do with an asteroid that flew past Earth this weekend.

At the time of the explosion, the object known as 2014 RC was about as far away as the moon, Johnson said. 2014 RC's passage close to the planet happened about 13 hours later.

Cooke said there could be any number of alternative explanations, ranging from ordinance to "someone out blowing things up".