By Phil Stewart

WASHINGTON (Reuters) - The United States has decided to delay a long-planned missile test scheduled for next week out of California "to avoid any misperception or miscalculation," given tensions with North Korea, a senior U.S. defense official said on Saturday.

The unusual precaution by the United States follows a barrage of hostile rhetoric from North Korea - including the threat of open war - that has created jitters in South Korea's financial markets.

It also came after reports in the South that Pyongyang, under its 30-year-old leader, Kim Jong-un, had moved two medium-range missiles to a location on its east coast.

The White House said on Friday it would "not be surprised" if the North staged another missile test. At the same time, officials have said there are no signs Pyongyang is gearing up for war, such as large-scale troop movements.

The U.S. decision will delay a test of the Minuteman III intercontinental missile, which had been scheduled for next week out of Vandenberg Air Force Base in California.

"This is the logical, prudent and responsible course of action to take," the official said, speaking on condition of anonymity.

The U.S. official said the test had been unconnected to "anything related to North Korea" and added that another test launch could be expected next month. The United States remained fully prepared to respond to any North Korean threat, the official said.

Analysts are looking anxiously ahead to April 15, the birthday of Kim Il-sung, North Korea's founder and the grandfather of its current leader, Kim Jong-un. The anniversary is a time of mass celebrations, nationalist fervor and occasional demonstrations of military prowess.

EMBASSIES STAYING PUT

North Korean authorities have told diplomatic missions they could not guarantee their safety from next Wednesday - after declaring that conflict was inevitable amid joint U.S.-South Korean military exercises due to last until the end of the month.

Still, staff at embassies in North Korea appeared to be remaining in place on Saturday despite the appeal.

Most countries saw the appeal to the missions as little more than strident rhetoric after weeks of threats by North Korea to launch a nuclear strike on the United States and declarations of war against the South.

But Russia said it was "seriously studying" the request.

A South Korean government official expressed bewilderment.

"It's hard to define what is its real intention," said the official, who asked not to be identified. "But it (North Korea) might have intensified these threats to strengthen the regime internally or to respond to the international community."

The United States is walking a difficult line, seeking to assure allies it will defend them in a crisis while trying to avoid further escalating tensions.

Initially, Washington used the drills with South Korea as an opportunity to demonstrate that commitment, including flying two B-2 stealth bombers over the Korean peninsula in March. The Pentagon also announced new or expanded missile defense systems in Alaska and Guam.

But the officials have told Reuters the United States will likely be less public about the drills in April, perhaps giving North Korea space to wind down its rhetoric. The latest decision to delay the U.S. missile test was also described as a prudent step.

"This test ... has been delayed to avoid any misperception or miscalculation in light of recent tensions on the Korean peninsula," the official said.

Shares in South Korea slid on Friday, but analysts said much of the decline was linked to the Bank of Japan's monetary easing policies and one analyst said further major falls were unlikely.

Most Korea watchers believe Kim is a rational actor who understands his military is no match for Seoul and its U.S. ally and that straying too far from historic North Korean practices could jeopardize his own political survival.

(Additional reporting by Jane Chung in Seoul,; Editing by Peter Cooney)