BAGRAM, Afghanistan >> The top U.S. military officer said today the Pentagon had bolstered its missile defenses and taken other steps because he "can’t take the chance" that North Korea won’t soon engage in some military action.

Heightened tensions with North Korea led the United States to postpone congressional testimony by the chief U.S. commander in South Korea and delay an intercontinental ballistic missile test from a West Coast base.

North Korea, after weeks of war threats and other efforts to punish South Korea and the U.S. for joint military drills, has told other nations that it will be unable to guarantee diplomats’ safety in the North’s capital beginning Wednesday.

U.S. Gen Martin Dempsey, the Joint Chiefs of Staff chairman who just wrapped up a visit to Afghanistan, was asked in an Associated Press interview whether he foresees North Korea taking military action soon.

"No, but I can’t take the chance that it won’t," he said, explaining why the Pentagon has strengthened missile defenses and made other decisions to combat the potential threat.

Dempsey said the U.S. has been preparing for further provocations or action, "considering the risk that they may choose to do something" on one of two nationally important anniversaries in April — the birth of North Korean founder Kim Il Sung and the creation of the North Korean army.

U.S. Gen. James Thurman, the commander of the 28,000 American troops in South Korea, will stay in Seoul as "a prudent measure" rather than travel to Washington to appear this coming week before congressional committees, Army Col. Amy Hannah said in an email today to the AP.

Thurman has asked the Senate Armed Services Committee, the House Armed Services Committee, and the House Appropriations subcommittee on defense to excuse his absence until he can testify at a later date.

Dempsey said he had consulted with Thurman about the rising tensions on the Korean peninsula.

Dempsey said both Thurman and South Korea’s Joint Chiefs of Staff chairman, Gen. Jung Seung-jo, decided it would be best for them to remain in Seoul rather than come to Washington. The Korean general had planned to meet with Dempsey, the U.S. Joint Chiefs of Staff chairman, in mid-April for regular talks.

Dempsey said that instead of meeting in person with Thurman and Jung in Washington, they will consult together by video-teleconference.

The Pentagon has postponed an intercontinental ballistic missile test that was set for the coming week at Vandenberg Air Force Base in California, a senior defense official told the AP on Saturday.

The official said U.S. Defense Secretary Chuck Hagel decided to put off the long-planned Minuteman 3 test until April because of concerns the launch could be misinterpreted and exacerbate the Korean crisis. Hagel made the decision Friday, the official said.

North Korea’s military said this past week that it was authorized to attack the U.S. using "smaller, lighter and diversified" nuclear weapons. North Korea also conducted a nuclear test in February and in December launched a long-range rocket that could potentially hit the continental U.S.

The U.S. has moved two of the Navy’s missile-defense ships closer to the Korean peninsula, and a land-based system is being deployed to the Pacific territory of Guam later this month. The Pentagon last month announced longer-term plans to strengthen its U.S.-based missile defenses.

The defense official, who was not authorized to speak publicly about the Minuteman 3 test delay and requested anonymity, said U.S. policy continues to support the building and testing of its nuclear deterrent capabilities. The official said the launch was not put off because of any technical problems.

Dempsey said he was not familiar with details of the Minuteman decision because he was traveling in Afghanistan.

But, he said, "it would be consistent with our intent here, which is to do what we have to do to posture ourselves to deter (North Korea), and to assure our allies. So things that can be delayed should be delayed."

A South Korean national security official said today that North Korea may be setting the stage for a missile test or another provocative act.

Citing North Korea’s suggestion that diplomats leave the country, South Korean President Park Geun-hye’s national security director said the North may be planning a missile launch or another provocation around Wednesday, according to presidential spokeswoman Kim Haing.

In Washington, an adviser to President Barack Obama said "we wouldn’t be surprised if they did a test. They’ve done that in the past."

Aide Dan Pfeiffer told ABC’s "This Week" that "the key here is for the North Koreans to stop their actions, start meeting their international obligations, and put themselves in a position where they can achieve what is their stated goal, which is economic development, which will only happen if they rejoin the international community."

He told "Fox News Sunday" that "the onus is on the North Koreans to do the right thing here," adding that "they are the source of the problem and the only way to solve this is for them to take a step back."

If they don’t, there will be consequences, Pfeiffer said.

"They will be able to further isolate themselves in the world, they will continue to further hurt themselves. The North Korean people are starving because of actions like the ones North Koreans are taking right now."

U.S. Sen. John McCain said the North’s young leader, Kim Jong Un, is playing a game of brinksmanship.

"In the past we have seen this repetitious confrontation, negotiation, incentives to North Korea to better behave, hopes that they will abandon their nuclear quest — which they never will, otherwise, they’d be totally irrelevant," McCain told CBS’ "Face the Nation."

"And so we’ve seen the cycle over and over and over again, for last 20 or 30 years. They confront. There’s crisis. Then we offer them incentives — food, money. While meanwhile the most repressive and oppressive regime on earth continues to function," he added.

McCain said China "does hold the key to this problem. China can cut off their economy if they want to."

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Associated Press writers Lolita C. Baldor, Philip Elliott and Erica Werner in Washington contributed to this report.