An undated photo released in January 2009 shows a missile firing drill at an undisclosed location in North Korea.
A photo identified by South Korean TV station KBS as Kim Jong-un, the third son of North Korean leader Kim Jong-il, at the age of 11. He is now 25.
Released June 8: North Korean leader Kim Jong Il gestures as he visits the Kosan Fruit Farm.
June 15: Tens of thousands of North Koreans gather at a rally at Kim Il Sung Square in Pyongyang, North Korea.
June 10: South Korean soldiers use binoculars to look at the North side from Imjingak, north of Seoul, South Korea.
June 9: South Korea heavy armored vehicles assemble during a military drill against a possible attack from North Korea in Paju.
2008 photo shows a surface-to-surface missile at a factory allegedly in Pyongyang, North Korea, during a visit by Burma's military government.
June 18: The South Korean Army Multiple Launch Rocket System fires during a military drill against a possible attack from North Korea.
With concerns rising about a possible North Korean long-range missile test this weekend, two independent scientists say the regime may be using an old Soviet ballistic missile to boost a rocket capable of reaching the West Coast of the United States.
North Korea is not known to have nuclear warheads and faces years of research and testing before building such a reliable weapon.
But the scientists say that if North Korea does have such a Russian-made ballistic missile in its arsenal, it could modify the rocket into a two-stage missile that could reach Seattle, Wash., carrying a 900-kilogram warhead, or San Francisco carrying a 700-kilogram charge.
The design of a long-range missile tested by North Korea last April "represents a very significant advance in rocket technology," said Massachusetts Institute of Technology professor Ted Postol and Union of Concerned Scientists' David Wright in a June 29 assessment published in the Bulletin of Atomic Scientists.
Using data and imagery from North Korea's April 4 launch, Postol and Wright calculated that the second stage of the North Korean rocket had the external dimensions, engine power and key features of an SS-N 6, a Soviet submarine-launched ballistic missile first deployed in 1968.
Their theory is at odds with U.S. officials' skepticism of the recent North Korean long-range missile launch, dismissed as a failure.
Missile expert and former U.N. arms inspector Mike Elleman cautioned against assuming that the similarities between the external dimensions of the North Korean second stage and the SS-N 6 mean that the two are the same technology.
But Elleman added that the coincidence is hard to explain.
Geoffrey Forden, another missile expert with MIT, sees merit in the Russian missile theory and believes North Korea may have its own production line for SS-N 6 missile components.