WASHINGTON, USA - A North Korean ship tracked by the US Navy and suspected of transporting weapons or military know-how in violation of UN sanctions has turned around, a Pentagon official said.

The official declined to provide details, including where the Kang Nam 1 ship - reportedly originally bound for Myanmar - could now be headed, but news reports out of South Korea suggested the ship may be returning home two weeks after it set sail June 17.

A diplomatic source speaking on condition of anonymity told the Korea Herald that the ship was 'near our waters,' which could suggest that sanctions were having an effect on reclusive North Korea.

'If the ship is on its way back, it would mean that Resolution 1874 is taking effect and causing the North to retreat,' Kim Tae-woo, vice president of the Korea Institute for Defense Analyses, told the newspaper.

The Kang Nam 1 quickly drew the attention of the US military under new UN sanctions designed to punish Pyongyang over its May 25 underground nuclear test.

The US ambassador to the United Nations, Susan Rice, confirmed Sunday that the United States was tracking the cargo ship.

'Obviously we're pursuing and following the progress of that ship very closely,' she told the CBS network.

'I'm not going to get into our operational details or what we might actually do on the high seas, if anything, or what allies and partners in the region might do.'

UN Security Council Resolution 1874, adopted in response to the May 25 nuclear test, calls for beefed up inspections of air, sea and land shipments going to and from North Korea, and an expanded arms embargo.

But a senior US lawmaker, Senate Republican Minority Leader Mitch McConnell, last week said the resolution had 'serious limitations' because it rules out the use of military force to back up the searches.