impasse at nuclear disarmament talks, while South Korea urged the communist nation to halt its provocations that have stoked tension on the peninsula.
The increased pressure from Washington and Seoul comes after a series of angry actions by the North responding to tougher policies by South Korea's new conservative government, which has refused to shy from criticizing Pyongyang or seek concessions for aid.
In the past week, North Korea has expelled South Korean officials from a joint Korean industrial zone, test-fired missiles, threatened to turn South Korea into "ashes" and labeled the new South Korean president a "traitor."
Washington also says the North has failed to provide a complete declaration of its nuclear programs by a deadline at the end of last year.
U.S. Assistant Secretary of State Christopher Hill said Wednesday he was waiting for a North Korean move "in the next few days" to end the impasse over the declaration. Hill said the U.S. had hoped to resolve that issue by the end of March, which passed without a resolution.
"We are very concerned about time," he said in Seoul after meeting South Korean diplomats.
Hill said North Korea's recent provocations were "directed at trying to upset the mood" in South Korea and called them "unhelpful." However, he said there was no need to overreact.
Meanwhile, South Korea's Defense Ministry sent a fax message to the North Korean military asking it to stop trying to rile its neighbor. The North's moves came after the South's top military officer said last week the country could strike suspected North Korean nuclear targets if there were signs of an imminent atomic attack.
As the North's "slander and its moves to raise tensions would never be helpful to peace and stability on the Korean Peninsula, we urge (the North) to immediately halt these activities," the ministry said. "Our side is always prepared for dialogue for inter-Korean peace and reducing tensions."
The statement came a day after a North Korean newspaper commentator leveled a blistering personal assault on South Korean President Lee Myung-bak. The North's main official newspaper blasted his pro-U.S. policies and said the impoverished country could live without South Korean aid, also warning of unspecified "catastrophic consequences" if the South failed to change course.
Lee's office has not yet directly responded that rhetorical attack, except to say that it was inappropriate to mention him by name.