U.N. secretary general warns North Korea after chemical attack

April 4 (UPI) -- The United Nations secretary general has called on North Korea to join the Chemical Weapons Convention, which bans member states from producing and using deadly agents like the chemical used to assassinate Kim Jong Nam in Malaysia.

U.N. Secretary-General Antonio Guterres and Organization for the Prohibition of Chemical Weapons Director-General Ahmet Uzumcu sent a letter to Pyongyang's Foreign Minister Ri Yong Ho on Thursday, according to South Korea's foreign ministry.

Ministry spokesman Cho June-hyuck said in the letter the U.N. chief stated, "All chemical weapons should be condemned and those who are involved should also be punished."

The letter is being delivered against a backdrop of international concern over the use of VX, a banned nerve agent, in the slaying of Kim Jong Un's older half-brother in Malaysia.

North Korea has denied involvement, but South Korean and Malaysian authorities have said North Korean agents may have been involved.

Signatories to the chemical weapons convention are required to dispose of all chemical weapons in their arsenal and open their facilities to international inspection.

Malaysia condemned the use of chemical weapons within its borders, but later cooperated with North Korea on the repatriation of Kim's body and the return of three North Korean officials, including a diplomat based in Kuala Lumpur once linked to the assassination.

North Korea. along with Egypt, Israel and South Sudan, is one of the few countries to not be in compliance with the chemical weapons convention.