US President Barack Obama on Thursday called on North Korea to end its "belligerent approach," as the world waited for Pyongyang to carry out an expected missile launch.

Obama, who spoke alongside UN Secretary General Ban Ki-moon after talks in the Oval Office, said "nobody wants to see a conflict" with the North, but that the United States is ready to take necessary measures to defend itself.

"We both agree that now is the time for North Korea to end the kind of belligerent approach that they've been taking," Obama said.

"It's important for North Korea, like every other country in the world, to observe basic rules and norms."

While the US president emphasized that Washington would "continue to try to work to resolve some of those issues diplomatically," he made it clear that the United States would be ready to face any eventuality and defend its allies.

"The United States will take all necessary steps to protect its people and meet our obligations under our alliances in the region," Obama said.

Earlier Thursday, Group of Eight foreign ministers including US Secretary of State John Kerry strongly condemned Pyongyang over its nuclear program, warning it would face further sanctions in the event of a missile launch.

North Korea has threatened to launch nuclear strikes against the United States and its allies in northeast Asia in retaliation over UN sanctions imposed over Pyongyang's December rocket launch and February nuclear test.