TOKYO, (CNN) -- Japan is mobilizing its missile defense system, and U.S. Navy ships are deploying to the Sea of Japan, as North Korea prepares to launch a rocket that is expected next month, officials said.
Japan's move, aimed at shooting down debris from the launch that might fall into its territory, is notable for a country with a pacifist constitution.
The U.S. ships are capable of shooting down ballistic missiles, a Navy spokesman said.
North Korea says it will launch a commercial satellite on top of a rocket sometime between April 4 and April 8. But other governments fear the North Koreans will actually put a long-range missile on top of the rocket.
The United States and Japan have been stepping up pressure on North Korea, hoping to head off the launch. 
Watch why the U.S. is 'very concerned' »
Russian Deputy Foreign Minister Alexei Borodavkin on Friday also urged North Korea to not launch the rocket, Russia's Interfax news agency reported.
Japan's military has two-pronged orders: to move destroyers carrying air-to-sea missiles to the Sea of Japan, which separates Japan and North Korea, and to send land-to-air missiles to northern Japan.
However, the probability of a missile successfully hitting a moving target without a known trajectory -- as in the case of debris -- is very low, Japanese Deputy Chief Cabinet Secretary Yoshitada Konoike said earlier this week.
If North Korea launches, the United States may have as little as five minutes to decide whether it is a threat and, if necessary, try to shoot it down. Watch more about the rising tensions »
The U.S. ships that are being moved to the Sea of Japan are "prepared to track a launch or more, if afforded," according to a U.S. Navy official who could not be named because of the sensitivity of the information.
The United States generally has a number of Aegis-capable ships in the Sea of Japan because of the threat posed by North Korea to launch missiles. The ships monitor the region and are designed to track and, if need be, shoot down ballistic missiles. See a satellite image of a North Korean launch site
The USS Hopper, a destroyer with the Aegis radar system aboard, was scheduled for a port call in Japan in coming days. But the port call was canceled and the ship will remain in the Sea of Japan ahead of the launch, the official said.
Two other U.S. Navy Aegis-capable destroyers, the USS Chaffee and USS McCain, were leaving the port in Sasebo, Japan, and were heading to South Korea for a ceremony in coming days, according to the U.S. Navy official with direct knowledge of the operations.
The U.S. Navy just wrapped up military exercises with the South Korean military, bringing a number of its ships into the region.
CNN's Kyung Lah and Mike Mount contributed to this report
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