WASHINGTON (AFP) - North Korea warned the United States before carrying out its third nuclear test, the State Department said on Tuesday, without specifying how much notice Washington was given.

"The DPRK did inform us at the State Department of their intention to conduct a nuclear test," State Department spokesman Victoria Nuland told reporters. "We were advised."

She stressed Washington had again told North Korea, also known as the Democratic People's Republic of Korea (DPRK), in the "strongest terms" that it opposed such plans.

"I'm simply going to tell you that it was prior to the event. I'm not going to get into any further details," she said, adding the warning came through the usual diplomatic channels.

Washington does not have diplomatic ties with Pyongyang and usually is represented in its diplomatic dealings with the North Korean leadership by Sweden.

The United States was now pushing for "consequences" at the United Nations, Ms Nuland said, agreeing that another layer of sanctions would be one option.

"Without getting ahead of policy, I would simply say that it is fair to say that we are looking at the full suite of options to try to get the DPRK to change course," Ms Nuland told journalists.

North Korea is already one of the most isolated countries in the world, and has been hit by a slew of international sanctions to try to force it to rein in its nuclear program.

But the US had found that internationally there was "quite a bit more that we could squeeze in terms of the DPRK's access to international finance ... in terms of cutting off its proliferation activities", MS Nuland said.

The UN Security Council met in emergency talks on Tuesday and all the powers backed a statement saying the North was in "grave violation" of council resolutions.

"In line with this commitment and the gravity of this violation, the members of the Security Council will begin work immediately on appropriate measures in a Security Council resolution," it added.