Three of the six countries not covered by the Chemical Weapons Convention are close to joining the agreement, the head of the world's chemical watchdog said Wednesday.

Speaking in Oslo the day after the Organisation for the Prohibition of Chemical Weapons (OPCW) formally received the Nobel Peace Prize, director general Ahmet Uzumcu said Angola, Myanmar and South Sudan "are very close."

"The three others have other concerns" which could be related to "regional reasons", he added during a meeting with Norwegian lawmakers broadcast by the NRK public service network.

The Chemical Weapons Convention -- which outlaws the production, stockpiling, and use of chemical weapons -- entered into force in 1997 and has 190 member countries including Syria, the latest nation to join in October this year.

Only six countries remain outside: Israel and Myanmar have signed the pact but not ratified it, while Angola, Egypt, North Korea and South Sudan have failed to do either.

During Tuesday's Nobel ceremony, both Uzumcu and the chairman of the Norwegian Nobel Committee, Thorbjoern Jagland, urged the remaining countries to join the convention.