TOKYO, June 8 (RIA Novosti) - North Korea is to close the shipping channels near the eastern port of Wonsan on the Sea of Japan in possible preparation for a missile launch, Japan's NHK television reported on Monday.

According to the report, Japanese security forces intercepted a North Korean radio announcement that said shipping was restricted for a 236-kilometer (147-mile) stretch of coast. The exclusion zone extends 100 kilometers from the coast into the Sea of Japan and will be in effect from June 10 through June 30.

Japanese Chief Cabinet Secretary Takeo Kawamura said on Monday that the reason for the closure was "unknown," adding that they could not rule out that "North Korea is planning to launch a ballistic missile."

A similar port closure was announced by North Korea on May 25, when it tested an underground nuclear explosion and launched a series of short-range missiles.

At an emergency meeting at the end of May the UN Security Council denounced Pyongyang's May 25 nuclear test as a violation of Resolution 1718 and the international nonproliferation regime. All members agreed to draft a new resolution on the North, already under a number of UN sanctions over its first nuclear test, carried out in 2006.

The six-nation talks involving North and South Korea, Russia, Japan, China and the United States, were launched in 2003 after Pyongyang withdrew from the Nuclear Nonproliferation Treaty (NPT).

Under deals reached in 2007, the North began disabling a nuclear reactor and other facilities at Yongbyon under international supervision, in exchange for economic aid and political incentives, which included the deliveries of fuel oil to Pyongyang.

However, in December last year, a round of six-nation talks ended in deadlock over a U.S. demand that nuclear inspectors be allowed to take samples out of the country from North Korean facilities for further analysis.

A Kremlin source told RIA Novosti earlier that the Russian leadership had no intention to turn a blind eye to North Korea's nuclear and missile tests, but was opposed to measures that would isolate Pyongyang.