The United States will pursue plans to construct a cost-effective and proven missile defense shield as long as a threat exists from Iran, U.S. President Barack Obama said on Sunday, hours after a missile launch by North Korea.
Obama said the need to construct a shield site in Europe would however fall away if the Iranian threat was removed.
Following are some details about the missile shield and the international politics surrounding it.
LESS SUPPORTIVE THAN BUSH
* The Obama administration had been cooler on the shield, which includes building a radar base in the Czech Republic and placing interceptor rockets in neighboring Poland, than the previous leadership of George W. Bush. It said it would put the plan under review
* The intention to construct sites in central Europe has angered Moscow, which called it a threat to its security and threatened to take retaliatory measures.
Both Poland and the Czech Republic are former Soviet satellite states that have joined the European Union and NATO since the fall of their communist governments in 1989.
* The plan also hit a major bump in the Czech lower house, where the government has a minority and the leftist opposition is against the shield.
THE PERCEIVED THREAT:
* Lieutenant General Henry Obering, head of the Pentagon's Missile Defense Agency (MDA), has said U.S. intelligence suggests that by 2015, Iran could follow North Korea's example and develop a long-range missile capable of striking the United States.
* The United States brought an earlier anti-missile umbrella, based in Alaska and California, on line in 2004 to protect against the perceived North Korean threat. The Czech and Polish sites were intended to augment that system.
* The United States say the shield's missiles are defensive only -- carrying no warheads -- and would in themselves be no match for Russia's nuclear arsenal.
* The system would use "hit-to-kill" technology in which an array of sensors and radar would detect an enemy missile in flight and guide a ground-based interceptor to destroy it.
* Without using explosives, the interceptor would ram an incoming warhead at a closing speed of 15,000 miles per hour in a process likened to hitting a bullet with another bullet in space.
* The MDA says tests show the technology is sound. But critics say the evidence is misleading, that many tests were made in controlled circumstances not resembling real attacks, and that more results are needed to prove the system works.
* The radar installation planned for the Czech Republic would aim its coverage toward the Middle East to detect a missile in flight and guide interceptor missiles into the trajectory of the approaching warhead.
* Washington plans to place 10 interceptor missiles with a range of up to 1,800 miles in Poland. The missiles would be housed in underground silos in an area about the size of a football field.
* Construction on both sites was earlier expected to begin in 2009, but there is no clear way ahead at the moment.
(Compiled by Jan Lopatka)