The U.S. military is tracking a flagged North Korean ship suspected of proliferating weapons material in violation of a U.N. Security Council resolution passed last Friday, FOX News has learned. 

The ship, Kang Nam, left a port in North Korea Wednesday and appears to be heading toward Singapore, according to a senior U.S. military source. The vessel, which the military has been tracking since its departure, could be carrying weaponry, missile parts or nuclear materials. 

"It is believed to be 'of interest,'" a senior U.S. official told FOX News. 

This is the first suspected "proliferator" that the U.S. and its allies have tracked from North Korea since the United Nations authorized the world's navies to enforce compliance with a variety of U.N. sanctions aimed at punishing North Korea for its recent nuclear test. 

The ship is currently along the coast of China and being monitored around-the-clock by air.

The apparent violation raises the question of how the United States and its allies will respond, particularly since the U.N. resolution does not have a lot of teeth to it. 

The resolution would not allow the United States to board the ship forcibly. Rather, U.S. military would have to request permission to board -- a request North Korea is unlikely to grant. 

North Korea has said that any attempt to board its ships would be viewed as an act of war and promised "100- or 1,000-fold" retaliation if provoked. 

If there is cause to pursue the ship, sources told FOX News the U.S. military would instead likely follow the slow-moving vessel until it goes into port to refuel. 

At that point, sources said, the U.S. military could request that the host country not provide fuel to the ship. 

One U.S. official said that the U.S. military could be waiting for the ship to distance itself from China before confronting it, to avoid agitating the Chinese. 

The Kang Nam is known to be a ship that has been involved in proliferation activities in the past -- it is "a repeat offender," according to one military source. The ship was detained in October 2006 by authorities in Hong Kong after the North Koreans tested their first nuclear device and the U.N. imposed a subsequent round of sanctions.

The latest tension follows a Japanese news report that North Korea may fire a long-range ballistic missile toward Hawaii in early July. 

Defense Secretary Robert Gates said Thursday the military is "watching" that situation "very closely," and would have "some concerns" if North Korea launched a missile in the direction of Hawaii. But he expressed confidence in U.S. ability to handle such a launch. 

Gates said he's directed the deployment of the Theater High Altitude Area Defense, a mobile missile defense system used for knocking down long- and medium-range missiles. 

"The ground-based interceptors are clearly in a position to take action. So, without telegraphing what we will do, I would just say ... I think we are in a good position, should it become necessary, to protect the American territory."

White House Press Secretary Robert Gibbs stayed mum on the suspect ship at Thursday's press briefing, commenting generally on the nature of the U.N. resolution. 

"There are some specific actions that have to be taken by countries who are near these ships, whose water these ships are in, ports that they might be destined for that are all part of this process," Gibbs said. "The White House feels comfortable and confident that we have an understanding of what this resolution does." 

FOX News' Jennifer Griffin and Justin Fishel contributed to this report.