TOKYO (AP) — President Barack Obama says he's not optimistic North Korea will shift away from its irresponsible behavior in the near future.

Obama says North Korea and its nuclear program comprise the most destabilizing situation in the Asia-Pacific region. He says if North Korean leaders are serious about being a normal nation, they must change their behavior.

Obama says he's confident that by working with Japan, South Korea and others, the U.S. can apply more pressure so that the North eventually chooses a different course. He says China's participation in pushing North Korea is critical.

Obama spoke at a news conference in Tokyo with Japanese Prime Minister Shinzo Abe (shin-zoh ah-bay). His comments come amid speculation that North Korea may conduct a fourth nuclear test while Obama is in Asia this week.