In a Dec. 7, 2007 file photo Libyan leader Muammar Qadhafi gestures while speaking during media conference at the University of Lisbon, in Lisbon, Libyan rebels took control of most of Tripoli in a lightning advance Sunday, Aug. 21, 2011, but the leader's whereabouts were unknown and pockets of resistance remained. - AP Photo

WASHINGTON: Libya's stock of chemical weapons, including over 10 tons of mustard gas, are under strict US surveillance, the Pentagon said Tuesday.

“We have been and continue to monitor chemical weapons sites,” spokesman Colonel David Lapan said.

Muammar Qadhafi’s regime joined the Organisation for the Prohibition of Chemical Weapons in 2004 after renouncing weapons of mass destruction in December 2003, but still had to eliminate 11.25 tons of mustard gas when the uprising to remove him from power began in February.

All 3,563 munitions -- such as bombs, shells and missiles -- that could serve as a carrier to distribute mustard gas have, however, been destroyed, according to the OPCW.

Mustard gas depots are located at Rabta, about 100 kilometers (60 miles) south of Tripoli and at the Ruwagha site in Al-Jufra, south of Sirte.

Under rules of the Chemical Weapons Convention, which Libya signed onto, such plants must remain closed or destroyed.

Mustard gas, also known as Yperite or sulfur mustards, can form large blisters or chemical burns on exposed skin and eyes, as well as cause bleeding and blistering within the respiratory system.

Asked about the heavy fighting now gripping Tripoli as rebels overran Qadhafi’s fortified Bab al-Azizya headquarters in a symbolic end to the strongman's 42-year iron-fisted rule, Lapan cautioned the situation remained “very fluid.”

“We believe the opposition forces control a large part of the country. Libya, and Tripoli in particular, are still very dangerous places,” the spokesman said.

“Until the Qadhafi regime ceases its attacks, it's not over.”