LOS ANGELES, June 28 -- An unmanned SpaceX's Falcon 9 rocket broke up on Sunday morning just minutes after liftoff, destroying the supplies it was carrying to the International Space Station.

"SpaceX Falcon 9 rocket launched at 10:21am ET. After liftoff, the launch vehicle failed," NASA announced.

The SpaceX Commercial Resupply Services 7 (CRS-7) mission took off right on time from Cape Canaveral Air Force Station in Florida. But shortly afterwards, video showed the rocket exploded over Florida.

The last readings from the vehicle were received two minutes and 19 seconds after launch, NASA spokesman George Diller said.

In a NASA press conference, SpaceX president and COO Gwynne Shotwell confirmed that a problem occurred in that general location, noting an overpressurization event in the liquid oxygen tank in the second stage of the rocket.

But SpaceX doesn't know yet what caused it. "Falcon 9 experienced a problem shortly before first stage shutdown," SpaceX CEO Elon Musk tweeted, "There was an overpressure event in the upper stage liquid oxygen tank. Data suggests counterintuitive cause."

The mission was to deliver the Dragon to the space station with more than two and a half tons of supplies, equipment and experiments, ranging from a new docking adapter for accommodating future U.S.-built spaceships to a virtual-reality headset for the station's crew.

The Dragon's payload includes food, oxygen and other much- needed basics and its loss will put even more pressure on the crew and mission planners.

"We are disappointed in the loss of the latest SpaceX cargo resupply mission to the International Space Station. However, the astronauts are safe aboard the station and have sufficient supplies for the next several months," NASA Administrator Charles Bolden said in a statement on the loss of the SpaceX Commercial Resupply Services 7 (CRS-7) mission.

Sunday's loss marked SpaceX's first failed mission to the space station, and extended a string of setbacks for space station resupply. The Dragon previously made six successful cargo runs under the terms of a 1.6 billion U.S. dollars contract with NASA, plus an initial demonstration mission in 2012.

"We will work closely with SpaceX to understand what happened, fix the problem and return to flight. The commercial cargo program was designed to accommodate loss of cargo vehicles. We will continue operation of the station in a safe and effective way as we continue to use it as our test bed for preparing for longer duration missions farther into the solar system," Bolden said.

This is the second failed station shipment this year. In April, a Russian cargo ship spun out of control and came down. And last October, Orbital Sciences Corp.'s supply ship was destroyed in a launch accident. Orbital's Antares and its Cygnus cargo capsule are not yet ready to go back into operation.

A Progress vehicle is ready to launch July 3, followed in August by a Japanese HTV flight. Orbital ATK, NASA's other commercial cargo partner, is moving ahead with plans for its next launch later this year.

The news that the SpaceX rocket has exploded moments after lift off from its base in Florida has disappointed many around the globe looking forward to the next stage in space exploration.

"Watched Dragon launch from space station Sadly failed. Space is hard," tweeted NASA astronaut Scott Kelly, who's currently the commander of the International Space Station and in the midst of an effort to live for more than a year in space.

After stage separation, the first stage of Falcon 9 was supposed to attempt a landing on a platform about 345 kilometers downrange in the Atlantic, but the flight never got that far.

"This is a reminder that spaceflight is an incredible challenge, but we learn from each success and each setback. Today's launch attempt will not deter us from our ambitious human spaceflight program,"Bolden said.