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North Korea conducted its third nuclear test Tuesday, the latest step in a years-long effort to develop nuclear weapons. Experts believe the country remains far from having a nuclear-armed missile that could threaten the United States, which would require an accurate long-range rocket and a nuclear warhead that could be mounted on it. Here is a look at North Korea's progress so far:

1998:

— ROCKET LAUNCH (August): This early launch gets the world's attention, because it goes well beyond North Korea's known capability. The rocket, which hurtles over Japan, has an estimated potential range of 1,550 miles (2,500 kilometers), but accuracy is reportedly poor with no meaningful strike capability.

2006:

— ROCKET LAUNCH (July): A three-stage rocket with a potential range of 4,100 miles (6,700 kilometers) fizzles soon after liftoff, the U.S. and South Korea say. North Korea has never acknowledged the launch.

— NUCLEAR TEST (October): North Korea detonates a nuclear device for the first time, but the yield is a very low 0.5 to 1 kiloton.

2009:

— ROCKET LAUNCH (April): This launch is a partial success, with two of the three stages pushing the rocket out over the Pacific. The third stage fails, and, despite North Korea's claims of success, no satellite is put into orbit, the U.S. says. The rocket dubbed Unha-2 represents a significant advancement over previous rockets, according to experts.

— NUCLEAR TEST (May): Second detonation of a nuclear device is a partial success with a larger yield of 2 to 6 kilotons, but still below the 10 kilotons that experts consider a successful blast.

2012-13:

— ROCKET LAUNCH (April 2012): Launch of Unha-3 rocket, with a potential range of 6,200 miles (10,000 km), ends in embarrassing failure, splintering into pieces over the Yellow Sea soon after takeoff. Hours later, the country acknowledges the satellite failed to enter orbit in an announcement on state TV.

— ROCKET LAUNCH (December 2012): This time, the rocket succeeds in launching a satellite into space. Its range, though questioned by some experts, in theory puts the U.S. West Coast, Hawaii, Australia and eastern Europe within striking distance.

— NUCLEAR TEST (February 2013): North Korea says it detonates a miniaturized nuclear device. If true, this would be an advance, as North Korea needs to master the technology to make a nuclear device small enough to mount on a missile. Early estimates put the yield at 6 to 7 kilotons, but that has yet to be confirmed.