After weeks of intensifying warnings from Washington and threats by Pyongyang, US policymakers are hoping to stop the crisis from spiraling into war while still standing firm on North Korea.

North Korea is famous for its shrill proclamations but it has sent shudders in the United States, South Korea and Japan in recent days by brandishing nuclear war and apparently moving a missile to its east coast.

The United States took the unprecedented step of announcing last week a bomb test by its nuclear-capable B-2 stealth fighter, one of a series of moves meant partly as reassurance to the new administration in ally South Korea.

A senior US official insisted that such shows of force were needed to influence North Korea but said that the United States also wanted to climb down from the crisis and minimize the potential for a miscalculation.

"No one should think we're on the brink of war, at least at this point, and we have to do everything we can to avoid it," the official told AFP on condition of anonymity.

The official said the United States was committed to its annual joint maneuvers with South Korea -- which end in April and included the B-2 and other advanced jets -- but that it may "go a little less public with our exercise activities."

The Pentagon said Wednesday it would speed up stationing of ground-based THAAD missile-interceptor batteries to protect the US Pacific territory of Guam but characterized the move as defensive.

State Department spokeswoman Victoria Nuland denied any shift in tone but said that the situation "does not need to get hotter" and that the United States was open to a "different course" if North Korea acts differently.

Driving the concern, the United States knows little about Kim Jong-Un, a third-generation leader in his late 20s who since taking charge in late 2011 has met few foreigners other than basketball all-star Dennis Rodman.

Scott Snyder, a senior fellow at the Council on Foreign Relations, said the United States had likely already taken enough actions to make its message clear to North Korea, which in February defiantly carried out a third nuclear test.

But Snyder said Washington had little incentive to turn down the temperature when it appears that Pyongyang may not have completed its playbook.

"My impression is that the North Koreans have got the message. At this point, the problem is that the North Koreans are already on a set course of action," he said.

Bonnie Glaser of the Center for Strategic and International Studies said that the United States had more leeway on revealing military moves as the key stretch of its exercises with South Korea was winding down.

But she said the United States could not make gestures toward North Korea, other than continuing to state that the door is open for dialogue.

"We do not want to reward their threats and I don't think we should really be offering them anything new, absent any steps by them to start ratcheting down these tensions," she said.

Kurt Campbell, who stepped down in February as the top State Department official on East Asia, said that President Barack Obama's administration has deliberately sent a "dual message" on North Korea.

The administration has warned North Korea but highlighted that it saw little concrete military build-up by Pyongyang.

"I think they (the administration) are doing that in a way so that we don't have a set of circumstances where things escalate beyond a point where it can be effectively managed," Campbell said at Johns Hopkins University.

"This is one of the most dangerous parts of the world. It's a hair-trigger, heavily militarized (area) and so great care needs to be taken," he said.