By Jonathan Head
BBC News, Bangkok
The US believes the Kang Nam 1 could be heading to Burma
Burma has denied any link with a North Korean ship in the South China Sea.
US officials have said they believe the Kang Nam 1 could be heading to Burma, carrying weapons in defiance of a United Nations embargo.
Burma and North Korea ended diplomatic relations in 1983 after a bungled assassination attempt by North Korean agents killed 20 people in Burma.
But in recent years they are believed to be co-operating in a number of areas, including weapons supplies.
For the past week the Kang Nam 1 has made steady progress down the coast of China, closely shadowed by a US Navy destroyer.
Now the Burmese government has issued a statement denying that the Kang Nam 1 is heading there, although it also said it was expecting another North Korean ship to arrive with a cargo of rice this weekend.
Burma is believed to have bought significant quantities of conventional weapons from North Korea in the past few years.
Burma is also to believed be getting help in building a sophisticated complex of tunnels and bunkers for its military rulers.
A new UN resolution passed in the wake of North Korea's recent nuclear test empowers member states to inspect any North Korean ships - but the US Navy has so far not attempted to intercept the Kang Nam 1 on the high seas.
However the ship may be forced to refuel in Singapore - in which case the Singaporean authorities would face a dilemma over whether to try to inspect its cargo - a move North Korea has warned it would view as an act of war.