North Korea had notified the International Maritime Organization of some earlier rocket tests.

Another United Nations agency, the International Telecommunication Union, said Tuesday that it also had been notified by the North Koreans of an impending launch, but without specifying a date range. An agency spokesman, Sanjay Acharya, said it had been advised by Kim Kwang-chol, the North Korean minister of posts and telecommunications, that the satellite was designed to function for four years.

North Korea asserts that its rocket program is peaceful, intended to launch satellites to gather data for weather forecasting and for other scientific purposes. But after the country put a Kwangmyongsong satellite into orbit by using its Unha-3 rocket in December 2012, the United States worried that in the process, the North was also moving toward acquiring the ability to deliver a nuclear warhead on a long-range ballistic missile.

That Unha-3, a three-stage rocket, blasted off from the Tongchang-ri launching site near the country’s northwestern border with China. American and South Korean officials have been monitoring the site for signs of preparations for another rocket launch, especially after North Korea conducted the last nuclear test, its fourth, on Jan. 6.

The United States and its allies are working to muster international support for a new Security Council resolution imposing another round of sanctions against the North. They have expressed concern that the North might attempt a long-range rocket test in retaliation.

In a report published last Thursday on 38 North, a United States website specializing in North Korea, Jack Liu, an expert on North Korea’s rocket program, said it appeared to be “in the early stages of preparation for launching a space launch vehicle.” He used recent satellite images of the site for his analysis.

South Korean intelligence officials said that in its 2012 rocket launch, North Korea was actually testing a design for a ballistic missile that could eventually fly more than 6,200 miles with a warhead of about 1,100 to 1,300 pounds, putting the West Coast of the United States within range.