A senior US official in charge of financial sanctions on North Korea visited South Korea this week for talks, a foreign ministry official said Friday.

The official said Daniel Glaser, deputy assistant secretary of the treasury for terrorist financing and financial crimes, arrived Wednesday for a visit ending Friday along with Steven Mull, a senior US Foreign Service officer.

"They met foreign ministry officials and other authorities concerned to discuss the issue of non-proliferation," the official told AFP on condition of anonymity.

Yonhap news agency quoted a diplomatic source as saying the talks concerned financial sanctions against North Korea.

The North demands the removal of United Nations sanctions before it returns to six-party nuclear disarmament talks. It also wants the United States to agree to start discussions about a permanent peace treaty before the nuclear forum resumes.

The United States, South Korea and Japan say it must come back to the nuclear talks and reaffirm commitment to disarmament agreements before other matters are discussed.

Japan's chief nuclear negotiator Akitaka Saiki and his South Korean counterpart Wi Sung-Lac reaffirmed that stance when they held talks Friday in Seoul, a foreign ministry official told reporters.

They agreed the North must return to the talks without preconditions, and removal of sanctions could only be considered when there was significant progress in denuclearisation, Yonhap news agency quoted the official as saying.

The ministry official said the sanctions issue, rather than the peace treaty, appeared to be blocking resumption of the talks which the North quit last April, a month before it staged its second atomic weapons test.

The United States has led a drive to enforce tougher UN sanctions imposed on the North last June following its nuclear and missile tests.

These include closer inspections of cargo suspected of containing banned missile and nuclear-related items, a tighter arms embargo and targeted financial curbs to choke off revenue for nuclear and missile development.

Several banned shipments of weaponry from the North have been seized since then.

In the latest reported case South Africa last month told the UN Security Council that it seized a shipment of North Korean spare parts for tanks bound for Congo.