VIENNA (AP) — U.N. Secretary-General Ban Ki-moon has urged the U.S. and seven other nations to ratify the treaty banning nuclear weapons testing so that the agreement can take effect.

Ban was speaking Wednesday at 20th-anniversary commemorations of the Vienna-based CTBTO, the U.N. organization created to monitor adherence to the treaty.

But all 44 nations that participated in treaty negotiations and possess nuclear reactors must ratify the agreement before it enters into force. Besides the U.S., China, Egypt, India, Iran, Israel, Pakistan and North Korea, which has actively resumed testing, still need to do so.

Ban called on those countries "to sign and ratify the treaty without further delay."