FACTBOX-Planned U.S. missile shield in Europe

Aug 15 (Reuters) - Poland has agreed to host elements of a U.S. global anti-missile system meant to protect Europe and the United States from what Washington says is the potential threat of attack by Iran.

Agreement on the shield, which Moscow opposes, was signed on Thursday amid a crisis over Russian military activities inside Georgia, a U.S. ally.

Under the preliminary deal the United States would place 10 interceptor rockets at a base in northern Poland. In exchange, Washington has promised to boost Poland's air defenses. The agreement must be approved by both the U.S. and Polish governments as well as Poland's parliament.

The United States and the Czech Republic have already signed a pact for that central European country to host a radar system as part of the shield. The Czech Republic's parliament still has to approve that deal.

Moscow has said the missile defense system will threaten Russian security. President Dmitry Medvedev on Friday said the timing of the announcement showed the system was clearly aimed at Russia.

Following are some details about the missile shield.

THE PERCEIVED THREAT

* Lt. Gen. Henry Obering, head of the Pentagon's Missile Defense Agency, 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 Sates.

* 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 would augment that system.