An unmanned, privately-owned US space capsule which took supplies to the International Space Station splashed down safely in the Pacific on Tuesday, its mission completed.

"SPLASHDOWN!" owner SpaceX tweeted. "Welcome home!"

Its descent slowed by three large parachutes, the Dragon capsule dropped into waters 320 kilometers (200 miles) off the coast of Mexico. Ships set out to pluck it from the water.

The day started with crew using a robotic arm on the ISS to complete the delicate de-linking of the capsule after a mission of just over three weeks.

Dragon delivered 1,200 pounds (544 kilos) of food, scientific material and other equipment during SpaceX's second resupply mission to the space station, which currently has a crew of two Americans, three Russians and a Canadian.

The capsule returned to Earth much heavier than on its outbound journey, as it carried more than 2,600 pounds of equipment from experiments conducted on the ISS.

One was designed to study molecular changes to a small flowering plant in microgravity. A related study examined how the plant roots hold up in low-oxygen environments.

The Dragon's docking with the ISS in early March after it was launched from Cape Canaveral in Florida aboard a Falcon rocket was delayed by 24 hours because of a problem with the capsule's thrusters that was quickly resolved.

The voyage was the third mission by the private SpaceX -- whose name is short for Space Exploration Technologies -- to the ISS under contract with NASA. The first of the missions was a test flight.

The return also happened a day later than originally scheduled because of bad weather in the splash-down area.

NASA's mission control in Houston handled the uncoupling of Dragon from the ISS. SpaceX staff in Hawthorne, California were in charge of getting the capsule through the atmosphere and back to Earth, with communications and other support from NASA.

SpaceX made history when Dragon became the first commercial spacecraft in history to successfully attach to the International Space Station, in a May 2012 test flight.

Previously only four governments -- the United States, Russia, Japan and the European Space Agency -- had achieved this challenging technical feat.

SpaceX has now begun regular missions to the ISS, completing its first official resupply mission in October 2012.

NASA is relying on SpaceX and other commercial ventures to take over for its retired fleet of space shuttles, which last flew in July 2011.

Before SpaceX's successful mission in October, NASA had been relying on Russian spacecraft -- but the Soyuz craft does not have room for cargo on the return flight.

SpaceX says it has 50 launches planned -- both NASA missions and commercial flights -- totaling about $4 billion in contracts.

So far, SpaceX has only sent unmanned flights into orbit, but the company aims to send a manned flight within the next three or four years. It is under a separate contract with NASA to refine the capsule so that it can carry a crew.

NASA also has a $1.9 billion resupply contract for the station with Orbital Sciences Corporation, which will launch the first test flight of its Antares rocket from a base in Virginia in the coming weeks.