Singapore will take action against a North Korean ship that the United States is monitoring, if the vessel heads to its port with a cargo of weapons, the government said.

"Singapore takes seriously the proliferation of weapons of mass destruction, their means of delivery and related materials," said a spokeswoman from the Ministry of Foreign Affairs.

"If the allegation is true, Singapore will act appropriately." The US Navy is monitoring a vessel called Kang Nam at sea under new UN sanctions that bar North Korea from exporting weapons, including missile parts and nuclear materials.

Fox News quoted a senior US military source saying the ship appeared to be heading toward Singapore and that the navy destroyer USS John McCain was positioning itself in case it gets orders to intercept, according to a story on its website.

Singapore, a US ally, has the world's busiest shipping port, with most containers being trans-shipments between East and West, and it is also the world's top ship refueling hub.

Singapore government agencies could not give information on the current location of the ship.

"We don't know even whether she is coming to Singapore," said a source at the Maritime and Port Authority of Singapore, which is responsible for security in Singapore waters and at its port.

The US officials said the ship became "a subject of interest" after leaving a North Korean port on Wednesday.

The Kang Nam is the first ship to be monitored under the UN sanctions adopted last week after Pyongyang raised tensions by test-firing missiles, restarting a plant to produce arms-grade plutonium and conducting a nuclear test.

The US has deployed anti-missile assets to the Pacific in case Pyongyang launches more missiles, US officials have said.

North Korea's media on Saturday said it was not threatened by new sanctions after a UN committee said it was considering blacklisting more North Korea companies, and individuals, for supporting Pyongyang's nuclear and missile programs.

"It is foolish and ridiculous of our enemy powers to call for more sanctions and isolation... (do they think) it could make us even raise our eyebrows one bit?" North Korea's Rodong Sinmum newspaper said in a commentary.

"If they point a gun at us, we will get back with a cannon. If they point a cannon, we will point missiles and for sanctions, we will give them revenge. Getting back with a nuclear weapon for a nuclear weapon is what we do."

• N.Korea defiant over sanctions threat