The US has delayed an intercontinental ballistic missile test scheduled for next week, defence officials say.
The Minuteman 3 test was put off over concerns it could be misinterpreted by North Korea, amid fears of a conflict.
It could be postponed until May, in what correspondents say will be portrayed by Pyongyang as a victory.
North Korea has issued a series of unusually strong threats since it was sanctioned by the UN in March for carrying out a third nuclear test.
It has threatened nuclear strikes on the US, formally declared war on the South, and pledged to reopen a nuclear reactor in defiance of UN Security Council resolutions.
A Pentagon official said the US wanted to "avoid any misperception or miscalculation" that might result from the test.
US and South Korean officials have sought to play down fears of a conflict on the Korean peninsula in recent days.
The BBC's John Sudworth in Seoul says Pyongyang will likely use the delay to its advantage in propaganda, and say the US has been forced to climb down in the face of resilience from the North Korean army.
The North Korean media are full of images of military preparedness, he adds, intended to rally people behind the leadership.
On Friday, North Korea warned it would not be able to guarantee the safety of embassy staff in the event of a war, but no foreign governments have announced plans to evacuate their embassies.
Many of North Korea's angry statements have cited annual military exercises between US and South Korean forces as provocation.
The US flew nuclear-capable B2 and B52 bombers over the South as part of the drill, and has since deployed warships with missile defence systems to the region.
This week, the North reportedly moved at least one missile to its east coast. It has threatened to strike the Pacific island of Guam, where the US has a military base.
North Korea's missiles have the capability to carry nuclear warheads, but the country is not yet thought to have developed such warheads.
Many observers say that North Korea's belligerent rhetoric appears intended for a domestic audience and at shoring up the position of Kim Jong-un, who came to power after his father's death in December 2011.
However, they also say that knowledge of the North's political calculations risk is limited, and the risk of a major escalation has increased amid the heightened tension of recent weeks.
Our correspondent adds that Pyongyang sees itself as vulnerable, having seen the upheaval in countries like Syria and Iraq, and is using the threat of nuclear weapons to protect itself.