U.S defense officials say the Obama administration is making major adjustments to its plans for a missile defense system in Poland and the Czech Republic.

A Pentagon spokesman Geoff Morrell says the change will better protect U.S. forces in Europe and America's allies from an Iranian short- or medium-range missile threat.  He said the U.S. has concluded that Iran is less focused on developing the long-range missiles for which the system was originally developed.

Earlier, Czech Prime Minister Jan Fischer said U.S. President Barack Obama had informed him the United States will not build the system, in a late Wednesday telephone call.

Former U.S. President George W. Bush first proposed placing interceptor missiles in Poland and guidance radar in the Czech Republic as a defense against Iranian missiles.

In Moscow, a Russian Foreign Ministry spokesman said his country would welcome such a change.

Russia had called the planned system a threat to its security.  It also was upset that the system was to be built in two former Soviet allies.

The news comes days before Mr. Obama will meet with Russian President Dmitri Medvedev at the United Nations General Assembly in New York, and a meeting of 20 of the world's most industrialized nations in Pittsburgh, Pennsylvania.

The Obama administration is said to be considering a handful of alternatives to a missile defense system in eastern Europe, including deploying shorter-range missile interceptors. 

Some information for this report was provided by AFP, AP and Reuters.