Libya's stockpiles of sulphur mustard agent and chemicals used to make weapons are intact and were not stolen during the uprising that toppled Muammar Gaddafi, weapons inspectors said Friday.

They said destruction of the materials would resume as soon as possible.

However, The Hague-based Organisation for the Prohibition of Chemical Weapons (OPCW) said the Libyan authorities had advised it on November 1 that further stocks of what are believed to be chemical weapons had been found and that Libya would make a new declaration of its stocks soon.

An OPCW inspection team found that the full stockpile of sulphur mustard and ingredients for making chemical weapons were intact at the Ruwagha depot, in southeast Libya, it said.

After Libya joined the Chemical Weapons Convention in 2004, it had to declare all of its chemical warfare materials and agree to destroy them.

The former Libyan government declared 25 metric tonnes of bulk mustard agent and 1,400 metric tonnes of precursor chemicals used to make chemical weapons, the OPCW said.

It also declared more than 3,500 unfilled aerial bombs designed for use with chemical warfare agents such as sulphur mustard and three chemical weapons production facilities.

The destruction program was halted in February 2011 because of a technical malfunction at the facility, after only part of the stocks had been destroyed, the OPCW said.

The inspectors returned at the invitation of the new Libyan government and with its full cooperation, the OPCW said, adding they would return to complete the destruction as soon as the facility was up-and-running again.

The OPCW will continue to work with the Libyan authorities to verify and destroy any newly declared stocks, it said.

The abandonment or disappearance of some Gaddafi-era weapons has caused international concern that such firepower could erode regional security if it falls into the hands of Islamist militants or rebels active in North Africa. Some fear they could be used by Gaddafi loyalists to spread instability in Libya.

The New York-based Human Rights Watch last month urged Libya's ruling National Transitional Council (NTC) to take action on large numbers of heavy weapons, including surface-to-air missiles, it said were lying unguarded more than two months after Gaddafi was toppled in a civil war.

U.N. Secretary-General Ban Ki-moon Wednesday said the United Nations would send experts to Libya to help ensure nuclear material and chemical weapons did not fall into the wrong hands.

(Reporting By Sara Webb; Editing by Janet Lawrence)