A Libyan rebel holds a Kingdom of Libya flag at Bab Al-Aziziya compound in Tripoli August 23, 2011.

A Libyan rebel holds a Kingdom of Libya flag at Bab Al-Aziziya compound in Tripoli August 23, 2011. Joyful Libyan rebels overran Muammar Gaddafi's Tripoli bastion on Tuesday, seizing weapons and loot and destroying symbols of a 42-year dictatorship they declared was now over as they set about hunting down the fallen ruler and his sons. REUTERS/Louafi Larbi

Rebel forces reportedly took control of Muammar Qadhafi’s fortified Bab al-Aziziya command base in Tripoli today as they further consolidated control of the capital. Confusion reigned amid reports that Qadhafi’s son Seif al-Islam, whom the opposition Transitional National Council had claimed to detain, apparently roamed free inside Tripoli rallying support for the regime.

As the murky situation in Tripoli gradually is sorted out, the United States must remain focused on the long-term goal of helping Libyans build a free, stable, and democratic Libya that will be an ally against terrorists. In the immediate aftermath of Qadhafi’s fall, Washington also must vigilantly ensure that his regime’s chemical weapons stockpiles and other dangerous weapons are secured with as much cooperation as possible from Libya’s new government, to prevent them from falling into the hands of terrorists. Senator John McCain (R–AZ) today called for urgent action to find and secure Libyan chemical weapons stockpiles.

The Qadhafi regime reportedly had 10 tons of mustard gas, much of it stored at an arms depot south of Sirte, near Qadhafi’s hometown. NATO forces have been closely monitoring the depot, which appears to be well-guarded by regime forces, but action must be taken soon to prevent the contents from being moved by Qadhafi diehards or looted by local civilians, Islamist militias, or the disorganized rebel army.

In addition to the mustard gas, the regime also had large quantities of precursor chemicals necessary for the production of nerve gas, which had not yet been destroyed after Libya’s 2004 agreement to dismantle its weapons of mass destruction. The regime also retained hundreds of tons of uranium yellowcake, the raw material from which the enriched uranium used in a nuclear weapon eventually could be produced.

Another high priority is finding and securing such dangerous weapons as anti-aircraft missiles known as MANPADS (Man-Portable Air Defense Systems). The Libyan army had large quantities of Soviet-era SA-7 shoulder-fired anti-aircraft missiles, which could pose a significant threat to commercial airliners if they are transferred to terrorist groups.

As the United States and its allies work to contain the potentially dangerous spillover effects of Qadhafi’s downfall, they must cooperate as closely as possible with Libya’s Transitional National Council. This must include discreet and urgent cooperation in finding, securing, and eventually removing lethal legacies of Qadhafi’s rule to prevent them from being recycled for use in the arsenals of terrorist groups.