TOKYO, August 1 (RIA Novosti) - Radioactive contamination could delay the work of experts from the UN nuclear watchdog to seal North Korea's nuclear facilities, shut down by Pyongyang under a disarmament deal agreed in Beijing in February, the Kyodo news agency said Wednesday.

The agency cited sources at the International Atomic Energy Agency (IAEA) as saying that traces of radiation have been detected at a an operational five-megawatt nuclear reactor and a plutonium-extraction plant in Yongbyon, 100 kilometers (60 miles) north of the capital Pyongyang.

IAEA experts arrived in North Korea in July to put seals and install monitoring equipment at five North Korean nuclear facilities by mid-August as part of an international effort to fold Pyongyang's nuclear program.

The IAEA officials said the contamination did not pose any threat to the environment, but would delay their work until the end of August because the inspectors had to decontaminate the facilities before installing the monitoring equipment and seals.

"Their [North Korean] nuclear safety standards differ from our standards," Kyodo quoted an IAEA experts as saying.

The Yongbyon complex consists of an operational five-megawatt nuclear reactor, a plutonium-extraction plant, a nuclear fuel production facility and research labs. The site also contains a 50-megawatt reactor whose construction was suspended under a 1994 nuclear deal with the United States.

The latest round of six-party talks on North Korea's nuclear disarmament ended July 20 without setting a deadline for the next steps in preventing the country from developing nuclear weapons, but participants reaffirmed their commitment to push forward with the process.

Envoys from China, Japan, Russia, the U.S. and the two Koreas have agreed to schedule meetings for working groups to discuss how to disable North Korea's nuclear facilities by the end of August and to hold the next round of six-party talks on North Korea's nuclear program in early September, followed shortly thereafter by a ministerial meeting.