SEOUL, South Korea — North Korea said on Tuesday that it had completed preparations to launch a satellite into orbit, as South Korea and other Asian nations told their airlines and ships to change their routes to avoid the North Korean rocket.

South Korea had previously refrained from issuing such directions while it joined its allies, particularly the United States, in urging North Korea to cancel the launching, scheduled for sometime between Thursday and Monday. They said it violated aUnited Nations Security Council resolution prohibiting North Korea from testing intercontinental ballistic missile technology.

But the North has remained defiant, and has placed the three-stage Unha-3 rocket at its launching pad.

“All the assembly and preparations of the satellite launch are done,” The Associated Press quoted Ryu Gum-chol, a senior North Korean space official, as saying during a news conference for visiting foreign journalists in the North Korean capital, Pyongyang.

Mr. Ryu said North Korea would launch the satellite as scheduled.

When asked about the chances of persuading North Korea to change its mind, Victoria Nuland, a spokeswoman of the United States State Department, said on Monday: “We’re not in the hope business here. We’re simply making clear we think this would be a very bad idea.”

In Moscow, the RIA Novosti news agency quoted a Foreign Ministry spokesman, Alexander Lukashevich, as saying that Russia viewed North Korea’s plans as “an example of ignoring decisions of the U.N. Security Council.”

As North Korea looked determined to press ahead, Philippine Airlines said it would change the paths of a dozen of its flights from the United States, Japan and South Korea so that they could stay clear from the North Korean rocket’s trajectory.

Japan Airlines and All Nippon Airways also planned to reroute flights connecting Tokyo to Manila, Jakarta, Indonesia, and Singapore.

South Korea’s Ministry of Land, Transport and Maritime Affairs said that it had ordered 22 Korean Air and Asiana Air flights to the Philippines to make detours between Thursday and Monday. Korean Air will also redirect two flights connecting Beijing and the South Korean island of Jeju.

North Korea told international aviation authorities that its rocket would blast off from its launching station near its northwestern border with China between 7 a.m. and noon and fly southward. Its first-stage section is expected to fall in the sea about 90 nautical miles off Kunsan, a city on the South Korean west coast. The second-stage section is expected to hit the waters east of the Philippines.

The Philippines and South Korea urged fishing boats and other ships to avoid waters where rocket debris may fall. The South Korean ministry said it would broadcast warnings to all domestic and international ships traveling near the splashdown zones.

In Washington, Jay Carney, the White House spokesman, warned that if the North went ahead with the satellite launching, the United States would probably cancel promised food aid shipments and would “continue to do the things that we have been doing in the past to isolate and pressure North Korea.”

Over the weekend, South Korean intelligence officials told the media that North Korea appeared to be preparing for a third underground nuclear test. That reminded analysts in the region of what happened the last time North Korea launched a satellite, in April 2009.

The Security Council condemned the launching, and North Korea walked away from nuclear disarmament negotiations in protest and conducted its second nuclear test in May that year. That in turn led the Security Council to tighten sanctions, and North Korea countered by declaring that it had started enriching uranium.

In the 2009 launching, experts said the first two stages of the North’s Unha-2 launch rocket appeared to have worked but the third stage did not ignite. Looking at the photos filed by reporters from the North Korean launching site, they said that the North’s new Unha-3 rocket appeared very similar to the Unha-2, indicating that North Koreans were continuing to improve the technology they tested in 2009.