Senior U.S. diplomats pressed North Korea to halt its belligerent behavior and return to nuclear disarmament talks even as the isolated communist nation pushed ahead with preparations to launch a long-range ballistic missile.

U.S. Deputy Secretary of State James Steinberg and a team of top envoys visited Seoul during an Asian tour to seek a unified response to Pyongyang's May 25 underground nuclear test and subsequent missile launches. The U.N. Security Council meanwhile continued to discuss how to punish the North.

The latest missile, believed capable of reaching the U.S., was being assembled under cover at a newly completed facility in Dongchang-ni near China, according to South Korea's JoongAng Ilbo newspaper. Earlier reports said it could be ready for launch in a week or two.

The missile appears to be longer than the rocket that North Korea fired over Japan and into the Pacific on April 5, a South Korean government official told the newspaper.

North Korea said the April launch put a satellite into orbit. The U.S. and Japan disputed that, saying they believed the impoverished communist nation had test-fired an intercontinental ballistic missile. North Korea followed up with an underground nuclear test on May 25.

Washington has strongly criticized the North for its actions, and envoys visiting Seoul underscored that concern Wednesday.

"I think we have a common view that we need to take steps to make clear to the North that the path it's on is the wrong one," Steinberg told reporters Wednesday after talks with South Korea's vice foreign minister, Kwon Jong-rak.

But he added that if the North were prepared to change its course, Washington was ready to "enter an effective dialogue that will really lead to a complete and verifiable denuclearization of the peninsula."

Steinberg was in Seoul with a team of high-ranking envoys, including President Barack Obama's special envoy on North Korea, Stephen Bosworth.

Bosworth said he had "some confidence" that dialogue with the North could resume, but he did not elaborate on the basis for his optimism. He said the Obama administration had supported dialogue from the beginning, and that the North would ultimately understand it was the best route to take.

The U.S. envoys' tour took them to Japan, South Korea and China — all participants in earlier dialogue toward the denuclearization of the Korean peninsula, and considered key for any coordinated response to the North's latest actions.

The likelihood of unified Asian support remained uncertain. Japan has already come out in favor of tough sanctions, but South Korea has been more restrained because of fears of chaos on its northern border. China has also expressed hesitancy about strong sanctions.

China — Pyongyang's closest ally and main aid provider — is a key player in any action on the North, and Obama discussed the nuclear crisis with Chinese President Hu Jintao in a phone call early Wednesday, the official Xinhua News Agency reported.

New sanctions being considered against North Korea include curtailing its financial dealings with the outside world, freezing company assets and enforcing an arms embargo, U.N. diplomats said Wednesday.

But China and Russia, key allies of Pyongyang, have raised questions about some of the proposals, diplomats said on condition of anonymity because the consultations are private.

South Korea meanwhile moved to further coordinate its response with the U.S., its prime ally.

Foreign Minister Yu Myung-hwan left for Washington to consult with his counterpart and prepare for a June 16 summit between Obama and South Korean President Lee Myung-bak.

Reports have suggested that North Korea may try to time its next missile launch to coincide with the summit.

Tensions on the peninsula have been ramped up in recent days.

North Korea's military reportedly strengthened its defenses and conducted amphibious assault exercises along its western shore. South Korea, which has put its troops on high alert, sent a high-speed ship equipped with guided missiles to the area and bolstered its artillery batteries.

At the border village of Panmunjom inside the Demilitarized Zone separating the two Koreas, a military guide warned that tensions were running high.

"The possibility of armed provocation is higher than ever in the Joint Security Area," the South Korean military guide said. He did not provide his full name, saying he did not have permission to do so.

Complicating the matter, two American journalists, Laura Ling and Euna Lee from former Vice President Al Gore's Current TV media venture, were to go on trial in Pyongyang on Thursday. The reporters are accused of entering the country illegally and engaging in "hostile acts."

Some experts believe the North is using the trial and its nuclear and missile tests to strengthen its position in possible talks with the United States, and that it hopes to win concessions or much-needed economic aid.

"Since North Korea is faced with the benign neglect of the U.S., the best way to attract attention is to be hawkish," said analyst Lee Sang-hyun of the Sejong Institute think tank.