SEOUL, South Korea - A North Korean-flagged ship under close watch in Asian waters is believed to be heading toward Myanmar carrying small arms cargo banned under a new UN resolution, a South Korean intelligence official said Monday.

Still, analysts say a high seas interception -- something North Korea has said it would consider an act of war -- is unlikely.

The Kang Nam, accused of engaging in illicit trade in the past, is the first vessel monitored under the new sanctions designed to punish the North for its defiant nuclear test last month. The U.S. military began tracking the ship after it left a North Korean port on Wednesday on suspicion it was carrying illicit weapons.

A South Korean intelligence official said Monday that his agency believes the North Korean ship is carrying small weapons and is sailing toward the Myanmar city of Yangon.

The official, who spoke on condition of anonymity citing the sensitive nature of the information, said he could provide no further details.

Myanmar's military government, which faces an arms embargo from the U.S. and the European Union, reportedly has bought weapons from North Korea in the past.

The Irrawaddy, an online magazine operated by independent exiled journalists from Myanmar, reported Monday that the North Korean ship would dock at the Thilawa port, some 20 miles (30 kilometers) south of Yangon, in the next few days.

The magazine cited an unidentified port official as saying that North Korean ships have docked there in the past. The magazine's in-depth coverage of Myanmar has been generally reliable in the past.

South Korean television network YTN reported Sunday that the ship was streaming toward Myanmar but said the vessel appeared to be carrying missiles and related parts. The report cited an unidentified intelligence source in South Korea.

Kim Jin-moo, an analyst at Seoul's state-run Korea Institute for Defense Analyses, said the North is believed to have sold guns, artillery and other small weapons to Myanmar but not missiles, which it has been accused of exporting to Iran and Syria.

The U.N. sanctions, which toughen an earlier arms embargo against North Korea, ban the country from exporting all weapons and weapons-related material, meaning any weapons shipment to Myanmar would violate the resolution.

The Security Council resolution calls on all 192 UN member states to inspect North Korean vessels on the high seas "if they have information that provides reasonable grounds to believe that the cargo" contains banned weapons or material to make them. But that requires approval from the North.

If the North refuses to give approval, it must direct the vessel "to an appropriate and convenient port for the required inspection by the local authorities."

North Korea, however, is unlikely to allow any inspection of its cargo, making an interception unlikely, said Hong Hyun-ik, an analyst at the Sejong Institute think tank outside Seoul.

A senior U.S. military official told The Associated Press on Friday that a Navy ship, the USS John S. McCain, is relatively close to the North Korean vessel but had no orders to intercept it. The official spoke on condition of anonymity because of the sensitivity of the issue.

Any chance for an armed skirmish between the two ships is low, analysts say, though the North Korean crew is possibly armed with rifles.

"It's still a cargo ship. A cargo ship can't confront a warship," said Baek Seung-joo of the Korea Institute for Defense Analyses.

Tension on the Korean peninsula has been running high since the North's May 25 nuclear test, with Pyongyang and Washington exchanging near-daily accusations against each other.

President Barack Obama assured Americans in an interview broadcast Monday that the U.S. is prepared for any move North Korea might make amid media reports that Pyongyang is planning a long-range missile test in early July.

"This administration -- and our military -- is fully prepared for any contingencies," Obama said during an interview with CBS News' "The Early Show."

Still, ever defiant, North Korea declared itself a "proud nuclear power" and warned Monday that it would strike if provoked.

"As long as our country has become a proud nuclear power, the U.S. should take a correct look at whom it is dealing with," the country's main Rodong Sinmun said in commentary. "It would be a grave mistake for the U.S. to think it can remain unhurt if it ignites the fuse of war on the Korean peninsula."