TIMELINE - North Korea: climbdowns and tests

(Reuters) - North Korea said it successfully conducted its second nuclear test on Monday, a move seen as certain to further isolate the impoverished state.

North Korea is already under U.N. Security Council sanctions for its first nuclear test in 2006, which officials and analysts say was only partially successful.

Here is a timeline of the North's nuclear activities and international attempts to contain them.

* 1979: North Korea starts to build a 5-megawatt nuclear reactor at Yongbyon, aided by years of Soviet nuclear help.

* Dec 12, 1985: North Korea declares existence of the Yongbyon facility to the International Atomic Energy Agency (IAEA), joins the nuclear Non-Proliferation Treaty (NPT). Treaty requires IAEA inspectors have regular access for monitoring.

* 1986: Yongbyon begins operation.

* March 1993: North Korea rejects IAEA inspectors' request to see two undeclared sites and threatens to withdraw from the

NPT.

* June 1994: North Korea quits the IAEA, 20 years after it first became a member state.