WASHINGTON (AP) ― The United States is in discussions with close ally Japan about expanding a missile defense system in Asia, the top U.S. general said Thursday.

Gen. Martin Dempsey, chairman of the Joint Chiefs of Staff, was commenting on a Wall Street Journal report that the U.S. is discussing positioning an early warning radar in southern Japan, supplementing one already in place in the country’s north, to contain threats from North Korea and to counter China’s military.

The State Department, however, said the missile defense system is not directed against China.

Dempsey said no decisions have been reached on expanding the radar.

“But it’s certainly a topic of conversation because missile defense is important to both of our nations,’’ Dempsey told reporters at the start of a meeting with his visiting Japanese counterpart, Gen. Shigeru Iwasaki, at the Pentagon.

Japan has worked closely with the U.S. for several years on missile defense, and has both land- and sea-based missile launchers.

North Korea’s ballistic missiles are considered a threat to security in the Asia-Pacific region because of the risk of conflict erupting on the divided and heavily militarized Korean peninsula, and because of the secretive North’s nuclear weapons program. The long-range rockets it is developing have been test-fired over Japan and potentially could reach the U.S.

The North conducted its latest long-range rocket launch in April, defying a U.N. ban. The North said the launch was intended to send an observation satellite into space but it drew international condemnation as the rocket technology is similar to that used for ballistic missiles. The rocket disintegrated soon after takeoff.

U.S. defense planners are also concerned about China’s military buildup, including its missile capabilities. The U.S. wants to enhance its longstanding military presence in the region as part of a rebalancing of its forces after a decade of fighting in Afghanistan and Iraq. China views this as part of a strategy to contain its rise.

The State Department said the U.S. is taking a phased approach to missile defense in Asia, as it is in Europe and the Middle East.

``These are defensive systems. They don’t engage unless missiles have been fired,’’ department spokeswoman Victoria Nuland told a news conference. ``In the case of Asian systems, they are designed against a missile threat from North Korea. They are not directed at China.’’

She said the U.S. has broad discussions with China through military and political channels about the systems’ intent.