A confidential report by independent UN monitors to a UN Security Council sanctions committee, seen by Reuters, said they had investigated cases of ship-to-ship transfers of petroleum products in violation of sanctions and that the network behind the vessels was primarily based in Taiwan.

Self-ruled Taiwan, claimed by China as its own, is not a member of the United Nations but says as a responsible member of the international community it is committed to ensuring sanctions are enforced in a bid to rein in North Korea's nuclear and missile programmes.

In a statement sent to Reuters, Taiwan's Foreign Ministry said the government had proactively taken part in enforcing the sanctions and that its efforts had been recognised by the United States and international community.

As for reports of Taiwan nationals breaking the sanctions, the government would continue to keep a close watch, it said.

Taiwan "again calls on our people and companies not to carry out any financial or commercial activities that contravene relevant resolutions of the United Nations Security Council, to avoid facing sanctions", the ministry added.

Last month, a court in Taiwan released on bail a man prosecutors allege made false declarations in the case of a Hong Kong-flagged tanker suspected of transferring oil to North Korea in violation of international sanctions.

The UN Security Council in December unanimously imposed new sanctions on North Korea for a recent intercontinental ballistic missile test, seeking to limit its access to refined petroleum products and crude oil.