US Republicans clamored to paint North Korea's surprise nuclear test as yet another failure of Barack Obama's foreign policy Wednesday, rounding on the outgoing president as he faced a stern new overseas challenge.

"Our enemies around the world are taking advantage of Obama's weakness," White House contender Senator Marco Rubio said, blasting the 44th president for standing "idly by" as a "lunatic" leader in Pyongyang threatens international peace.

Republicans vying to replace Obama in 2017 have accused him, and his former secretary of state Hillary Clinton -- the Democratic presidential frontrunner -- of lacking resolve.

They say Obama's overly cautious foreign policy has created a void that the Islamic State group, Russia, China, Iran and now North Korea have stepped into.

It comes after North Korea said it had carried out a "successful" miniaturized hydrogen bomb test -- though experts are skeptical of the claim.

Senator Ted Cruz, another Republican White House candidate, said North Korea's test "underscores the gravity of the threats we are facing right now and also the sheer folly of the Obama-Clinton foreign policy."

"When we look at North Korea, it's like looking at a crystal ball. This is where Iran ends up if we continue on this same misguided path."

Obama came to office in 2009 vowing to extricate the United States from costly foreign wars, while signaling Washington would no longer rush headlong into every global crisis.

He has also engaged with US foes Iran and Cuba, popular bogeymen for Republicans on the campaign trail.

White House aides say Obama's policy is borne from a more steely eyed approach to the US national interest.

But they also admit that policy toward North Korea, which has seen three nuclear tests during Obama's presidency, has been less than a total success.

Obama's broad aim was to get reclusive Pyongyang to abandon its nuclear program, stop destabilizing the region and come back to the negotiating table.

"It is true that we have not achieved our goal," conceded White House spokesman Josh Earnest.

"But we have succeeded in making North Korea more isolated than ever before and the international community more united than ever before."

- Tough spot -

North Korea's latest actions leave the White House with a difficult balancing act.

On one hand, Obama needs to carefully craft a response with South Korea and Japan and, perhaps above all, China, North Korea's sole major ally.

"The question is, will Beijing react passively as it has in the past or will it eventually decide to get tougher with Pyongyang and let sanctions bite?" asked Duyeon Kim, a Seoul-based expert with the Carnegie Endowment for International Peace.

US National Security Advisor Susan Rice on Wednesday met the Chinese ambassador at the White House to measure Beijing's intent.

Obama is slated to speak to Japanese Prime Minister Shinzo Abe and South Korean President Park Geun-Hye later Wednesday.

Park has made a concerted effort to forge a close relationship with Chinese leader Xi Jinping and US officials will hope her newfound sway in Beijing can now be brought to bear.

Meanwhile, inside the United States, Republican demands for tough action point to public pressure on Obama's administration to show steel in the face of international threats.

A recent Economist/YouGov poll showed two-thirds of Americans are unhappy with the way Obama has handled foreign policy.

Earnest rejected Republican criticism as vote seeking.

"They're trying to win votes from conservative Republicans in a presidential primary," he said. "We've heard a lot of campaign rhetoric, but not a lot of specific, tangible suggestions about what should be done differently."

Despite the pressure on the White House and North Korea's seemingly ever-more potent military capabilities, Kim said a dramatic change in US policy was unlikely.

"The administration probably will not shift its current approach, especially with less than a year left of President Obama's term," she said.

"The next administration will need to devise an effective and proactive strategy or else Washington will be faced with some tough decisions."