The Obama administration will add 14 interceptors to a West Coast-based missile defense system, reflecting concern about North Korea's focus on developing nuclear weapons and its advances in long-range missile technology, officials said Friday.

Defense Secretary Chuck Hagel planned to announce the decision later Friday. It was first reported by Fox News.

In advance of Hagel's announcement, defense officials confirmed the decision on condition of anonymity because they were not authorized to discuss it publicly.

The Pentagon intends to add the 14 interceptors to 30 already in place in California and Alaska. That will expand the system's ability to shoot down long-range missiles in flight before they could reach U.S. territory.

James Miller, defense undersecretary for policy, said in a speech Tuesday that the Pentagon has the ability to deploy up to 14 additional missile interceptors, "if needed." He did not say in the speech that a decision had been made to do so.

Miller also said the Pentagon is studying three alternative sites for deploying still more interceptors in the U.S., if needed. He said that would provide options for building an interceptor base on the East Coast or adding more interceptors in Alaska, "should either approach become necessary due to further future increases in the threat from Iran and North Korea."

The threat of a missile strike from North Korea was the rationale for building the missile defense sites in Alaska and California during the administration of President George W. Bush. Technical difficulties with the interceptors slowed the pace at which they were installed in California and Alaska. "Our policy is to stay ahead of the threat - and to continue to ensure that we are ahead of any potential future Iranian or North Korean ICBM (intercontinental ballistic missile) capability," Miller said in Tuesday's speech.

Miller noted that last December, North Korea launched a satellite into space, demonstrating its mastery of some of the same technologies required for development of an intercontinental ballistic missile.

"Our concern about Pyongyang's potential ICBM capability is compounded by the regime's focus on developing nuclear weapons. North Korea's third nuclear test last month is obviously a serious concern for all nations," he said.

North Korea recently threatened to reduce Seoul to a "sea of fire" and stage pre-emptive nuclear attacks on Washington.

"North Korea's shrill public pronouncements underscore the need for the U.S. to continue to take prudent steps to defeat any future North Korean ICBM," Miller said in his speech on Tuesday.