SEOUL, South Korea -- American and South Korean troops increased alert levels on Wednesday as South Korea's foreign minister warned that North Korea could launch its medium-range Musudan missile "any time from now."
Although North Korea has tested many of its short-range Scud and medium-range Rodong missiles, it has never flight-tested the longer-range Musudan, believed to have a range of around 2,175 miles. A successful test of the missile would demonstrate the North's potential to hit not only South Korea but also all of Japan and targets as far away as the American military bases on the Pacific island of Guam.
"Based on intelligence we and the Americans have collected, it's highly likely that North Korea will launch a missile," Foreign Minister Yun Byung-se of South Korea told a parliamentary hearing on Wednesday, adding that such a test would violate United Nations resolutions banning the country from testing ballistic missiles. "Such a possibility could materialize at any time from now."
The American and South Korean troops raised their "Watchcon" level of vigilance, stepping up monitoring and intelligence-gathering activities, officials at the South Korean Defense Ministry said.
Adding to the concerns, North Korea often stages military provocations around important national anniversaries, and Monday is the birthday of North Korea's founder, Kim Il-sung, the grandfather of the current leader, Kim Jong-un.
Japan was also on guard for a potential North Korean missile launch, deploying PAC-3 missile interceptors in key locations around Tokyo as a precaution. The American military has moved two Navy missile-defense ships closer to the Korean Peninsula to monitor any North Korean missiles launchings and to intercept the missiles if they threaten the American bases or Washington's allies in the region.
South Korean military officials said that they had detected the movements of not only the Musudan but also Scud and Rodong missiles to the North's east coast, indicating that the North might fire those missiles together, as they had done before.
The Associated Press, which has a bureau in the North Korean capital, Pyongyang, reported on Wednesday that despite warnings from their leaders of impending nuclear war, residents of Pyongyang gave no sense of panic, with people planting trees and dancing in the plazas ahead of the holiday.
The North Korean warnings also appeared to have little or no effect on the small Pyongyang community of foreign diplomats, who had been admonished by the host government last week that it could not guarantee their safety as of Wednesday and should consider evacuating.
A spokeswoman for Catherine Ashton, the top foreign policy official at the European Union, said in Brussels that despite North North Korea's "aggressive rhetoric, we judge that the situation on the ground does not justify evacuation or relocation." The spokeswoman, Maja Kocijancic, said this message had been delivered via the Swedish Embassy to North Korea's Foreign Ministry, along with a reminder that under the Vienna Convention on Diplomatic Relations, North Korea "has a continuing obligation in all circumstances to protect diplomatic missions and E.U. citizens."
Besides Sweden, the European Union members with embassies in Pyongyang include Britain, Bulgaria, the Czech Republic, Germany, Poland and Romania.
The military activity came as tensions continued to affect economic ties between the two Koreas. For a second consecutive day, North Korean workers did not turn up for work on Wednesday at the industrial complex the two Koreas had run jointly in the North Korean city of Kaesong. About 110 South Koreans returned home on Wednesday, reducing the number of South Koreans staying there to 297.
North Korea suspended operations at the factory park in response to ongoing joint American-South Korean military drills and United Nations sanctions imposed for its Feb. 12 nuclear test.
The money earned by North Korean workers at Kaesong has been a key source of badly needed foreign currency for the North Korean regime. Wednesday was a payday for North Korean workers, but with the North blocking anyone from the South from entering the industrial zone, South Korean factory owners had no way to pay their North Korean workers.
There were also signs that the tensions were starting to hurt tourism to the North. Officials in Dandong in northeastern China told tour operators to halt overland tourism into North Korea, local travel agents told Reuters.
Also Wednesday, South Korea officially blamed North Korea for launching a series of hacking attacks that paralyzed the computer networks of three broadcasters and three banks, as well as several government Web sites, in the South last month.
The findings by a joint investigation team that included government and civilian experts underscored a new dimension to North Korea's recent threats to attack the United States and South Korea. South Korean officials said their latest investigations confirmed that North Korea's cyberwarfare, once limited to the spreading of propaganda through the Web, was increasingly expanding into more disruptive hacking attacks.
"We have found enough evidence that these recent attacks and the attacks in the past originated in the same group," said Chun Kil-soo, an official at South Korea's Internet security agency, during a media briefing on Wednesday. "We believe North Korea was involved."
A new wave of cyberattacks started on March 20, when the computer networks of the banks and broadcasters went down. On May 26, similar attacks using malicious codes crashed the Web sites of several provincial governments and anti-North Korean activist groups.
South Korea's National Intelligence Service had suspected North Korea's involvement in at least six earlier hacking attacks reported in South Korea since 2008, including the massive disruptions that crashed South Korean government Web sites in 2009 and 2011.
While tracing the sources of the March attacks, South Korean investigators located six computers and 13 Internet Protocol addresses in North Korea, Mr. Chun said.
The experts identified 49 routing points, as well as 1,000 Internet Protocol addresses, in South Korea and 10 other countries as they traced the paths of the hackers who infiltrated their target networks as early as last June, planting malware there, Mr. Chun said. Many of the 76 malicious codes used in the attacks, routing points and Internet Protocol addresses were ones used in the earlier attacks that had been already blamed on the North, he added.
Rick Gladstone contributed reporting from New York.
Correction: April 10, 2013, Wednesday
This article has been revised to reflect the following correction: An earlier version of this article gave the incorrect date of cyberattacks that crashed the Web sites of several South Korean provincial governments and anti-North Korean activist groups. It was March 26, not May 26.world
This article originally appeared in The New York Times.