WASHINGTON—North Korea appears to have turned a corner in its goal of achieving mastery of ballistic missiles, U.S. officials and weapons experts said following its successful rocket launch early Wednesday, adding to pressure on the Obama administration to contain Pyongyang's arsenal.

A particular concern for U.S. officials is that Iran, which also is developing a nuclear program and long-range missiles, could take heart from its Asian ally's success and accelerate what the West suspects is a goal of developing a warhead. Pyongyang and Tehran have closely cooperated in developing missile systems for more than two decades, according to U.S. and Asian officials.

North Koreans dance in Pyongyang on Wednesday to celebrate their country's launch of a long-range missile. Xinua/Zuma Press

"Nothing that we're doing now in terms of sanctions or diplomacy or anything has stopped [Pyongyang]," said Victor Cha, who served as a top adviser on North Korea to President George W. Bush. "Counterproliferation now becomes much more important."

The United Nations Security Council condemned the North's launch of a three-stage rocket that Pyongyang claimed had placed a weather satellite into orbit earlier Wednesday. The launch appeared to be North Korea's first breakthrough following four largely unsuccessful tries since 1998.

U.S. officials said they believed the launch was cover for North Korea to further develop long-range missiles that could eventually carry nuclear warheads capable of threatening Washington's allies in Asia, and, potentially, the U.S. West Coast. Japanese authorities estimated the rocket's range at about 3,700 miles.

Pyongyang has conducted two nuclear tests over the past decade, and U.S. intelligence agencies estimate it has produced enough fissile material for as many as a dozen atomic bombs.

Officials are still assessing whether the object carried by the rocket achieved a stable orbit. Some U.S. officials described the satellite as slipping out of North Korea's control. But making a final determination will take days, according to an official at the U.S. Strategic Command, which is tracking the object. Should Pyongyang indeed lose control at times it could still re-establish it, the official said.

"I am not prepared to agree to the characterization of it being a stunning success by any means," said a U.S. official. "We are still assessing it, and I am not sure that [success] is where we are going to end up."

Regardless of the satellite's fate, the missile technology that placed it into orbit demonstrates a new level of sophistication.

The North Korean launch showed that Pyongyang has been able to correct earlier problems with multistage rockets, said Henry "Trey" Obering III, a retired Air Force lieutenant general and the former head of the U.S. Missile Defense Agency. "They are a major step closer to having an ability to threaten the continental United States."

The launch violated U.N. Security Council resolutions banning North Korean missile activity. U.S. and European officials said Wednesday that they would seek to use a new Security Council resolution to enact tougher financial sanctions on North Korean leaders and companies. They also said they would work to develop ways to more intrusively contain the spread of nuclear technology and an array of conventional weapons in and out of the secluded state.

The Security Council "must now work in a concerted fashion to send North Korea a clear message that its violations of U.N. Security Council resolutions have consequences," said the Obama administration's ambassador to the U.N., Susan Rice.

Still, critics of successive U.S. administrations said international sanctions and diplomacy have done little to prevent North Korea from steadily developing a nuclear weapons arsenal over the past three decades.

North Korea's Nuclear Ambitions

See developments in North Korea's nuclear-weapons arsenal and long-range missile program since the early 1990s.

They said the White House should move more aggressively to establish a missile-defense system in Asia to defend allies such as Japan and South Korea.

Some also said that the U.S. must be prepared to heighten air and maritime interdictions as well as covert actions against Pyongyang, including sabotage, to prevent it from mastering the technologies needed to place a nuclear warhead on a long-range missile.

Current and former U.S. officials are worried that the North's advances could fuel a further arms race in Northeast Asia. Japan is already seen as having a latent nuclear-weapons capability. South Korea is developing long-range missiles and has a vast civilian nuclear-power program that could be converted to military use.

These officials are also concerned that North Korea would be willing to export its nuclear-weapons technologies to networks of buyers in the Middle East and Asia.

Pyongyang has regularly exported missile technologies to Iran, Syria and Myanmar, according to U.S. and Asian officials. U.N. nuclear inspectors believe the North secretly built a nuclear reactor in eastern Syria that was destroyed by Israeli jets in 2007.

U.S. and allied intelligence services have intercepted shipments of North Korean missile components going into all three countries in recent months, according to U.S. and Asian diplomats. "North Korea has proven that it's willing to sell anything to anyone. They need the hard currency," said David Asher, who has tracked Pyongyang's arms trade both at the State Department and the Center for New American Security, a Washington think tank.

U.S. officials particularly worry that China could impede any efforts at the U.N. to choke off North Korea's weapons development.

Beijing has supported international diplomacy focused on containing North Korea's nuclear program, called the six-party talks. China has backed both previous U.N. resolutions sanctioning North Korean military officers and arms companies.

But China continues to provide significant financial assistance to Pyongyang and its new leader, Kim Jong Eun. And North Korea companies have used China as a base through which to procure and sell arms equipment, according to U.S. and Asian officials.

This week's launch, said Rep. Mike Rogers (R., Mich.), chairman of the House intelligence committee, should be a "wake-up call" to change U.S. policy toward North Korea. North Korea has already shared its nuclear and missile technology, and will spread long-range missile expertise as well, he said. "That's what makes this so dangerous," Mr. Rogers said. He said the Obama administration should press China to head off a nuclearized Korean peninsula.

The rocket launch, which occurred Tuesday night U.S. time, was monitored by American and Japanese military officials.

State media distributed an image, right, from the control center's monitors. kyodo/Reuters

U.S. officials said the Pentagon didn't attempt to intercept the rocket with missile-defense systems because it was never assessed to be a direct threat.

The Japanese also have missile-interception capabilities, officials said, but they decided the rocket didn't pose a direct threat to Japan, either.

If the rocket headed toward Hawaii, it could have been hit by the ground-based U.S. interceptors in Alaska, U.S. officials said. Had the missile threatened Japan or another target in Asia, the U.S. could have tried to intercept it with its Aegis-ship based missiles.

Gen. Obering said the U.S. doesn't have the ability, except under limited circumstances, to intercept a missile in its "boost" phase, while it is heading upward.

"The system is designed as a military system…to defend against an attack," Gen. Obering said. "So if a missile does not threaten a territory, the system does not want to waste an interceptor."

North Korea's state media first announced the flight about two hours after it occurred and, in later dispatches, called it "a great turn in developing the country's science, technology and economy by fully exercising the independent right to use space for peaceful purposes."

The apparent success of the launch is expected to help new leader Kim Jong Eun, just as North Korea is about to commemorate the first anniversary of the Dec. 17 death of his father, Kim Jong Il. The younger Mr. Kim is perceived by outsiders to be facing some internal dissension, particularly from military leaders who have lost some of their power in the year he has been in charge.


—Evan Ramstad, Dion Nissenbaum, Joe Lauria and Siobhan Gorman contributed to this article.