Most of Libya's missing stocks of shoulder-fired anti-aircraft missiles are still in the country but they need to be secured before they are smuggled to militants outside Libya, a U.S. official said on Monday.

Former Libyan leader Muammar Gaddafi had about 20,000 of the missiles. Many of them were looted during the conflict that ended his rule, prompting concern that they could end up in the hands of al Qaeda's north African branch.

The weapons, often referred to as MANPADS or 'man portable air defence systems', are favoured by militant groups because they are light and portable, relatively simple to use and can in theory bring down a civilian airliner.

Derrin Smith, an adviser to the U.S. government's inter-agency task force on MANPADS, said predictions that large numbers of the weapons would be taken out of Libya to al Qaeda's desert strongholds have not been realised.

It appears at this point that most of the Libyan MANPAD stocks continue to be in the hands of Libyan personnel. So we'll work with the government to recover those into centralised government inventory control, Smith told a news conference in the Algerian capital.

The bad news is that no one is certain what the exact number is that is outside government control and it will take some months of effort to come up with a reasonable number.

SECURE STORAGE

In the chaotic fighting to end Gaddafi's rule, local militias trying to overthrow him raided arms depots and took the weapons for themselves.

The militias are largely loyal to the Western-backed government now in power, but there are questions over how securely they are storing the weapons.

Security experts have said that MANPADS could be acquired by militants or smugglers and taken across Libya's porous southern borders into neighbouring Algeria, Mali, Mauritania and Niger.

Al Qaeda's north African branch, al Qaeda in the Islamic Maghreb (AQIM) is active in the Sahara desert, which straddles those countries. An AQIM commander has said his group exploited the Libya conflict to obtain weapons.

But Smith said shoulder-fired missiles, or their components, from Libyan stocks had so far not been found among arms shipments intercepted in the Sahara.

We have not had much indication of MANPADS yet moving through the region, he said after talks with Algerian officials.

There were some components of surface-to-air missiles that have been interdicted by ... regional countries. They did share the information with us, he said.

Expert analysis revealed those components were not related to the inventory or stocks in Libya. And none of the components that have been recovered at any of the borders were fully functioning.

He said that U.S. weapons specialists, working with the new Libyan government, had already catalogued some stocks of shoulder-fired missiles inside the country.

The bulk of the inventory are SA-7 older Soviet models of surface-to-air missiles, said Smith. Some of the missiles they have recovered were corroded and non-functional. Many of the others were still in their steel shipping containers and were fully functioning missiles.

(Reporting By Christian Lowe; Editing by Tim Pearce)