SpaceX and NASA are trying to investigate what went wrong after a Falcon 9 rocket exploded shortly after launch from the Kennedy Space Center in Florida on June 28.

Debris from the SpaceX Falcon 9 rocket falls through the sky after the rocket broke up during launch on a supply mission to the International Space Station. Source: NASAThe rocket exploded two minutes after lifting off on what had been a planned mission to resupply the International Space Station. Technicians are examining data down to the milliseconds before the explosion to find out what went wrong.

It was not immediately known whether the incident was an accident or if SpaceX triggered the explosion because it had gone off course.

Elon Musk, owner of SpaceX, tweeted, “There was an overpressure event in the liquid oxygen tank. Data suggests counterintuitive cause”.

Officials are calling the accident an anomaly.

"There's no negligence here, there's no problem with this. It just shows the challenges facing engineering and the challenges of space flight in general," says NASA associate administrator William Gerstenmaier.

At the International Space Station, three astronauts were waiting for the resupply rocket, but officials say there are enough supplies to last the crew until October.

Aerospace experts are quoted as saying that they do not believe the Falcon 9 design is to be blamed; the rocket has flown a total of 18 times. The June 28 explosion was the first for SpaceX since 2008 when the Falcon 1 did not reach orbit.

Officials expect the investigation to last several months.