NATO is condemning Libya's use of a scud missile in its battle against rebels who are advancing toward Tripoli to oust Libyan leader Moammar Gadhafi.

NATO spokeswoman Carmen Romero says the Gadhafi government's use of the short-range ballistic missile shows that it is “desperate” as the rebels close in on the capital. In a news conference Tuesday in Brussels, Romero said many civilians could have been killed when pro-Gadhafi forces used the missile to attack Brega on Sunday.

Meanwhile, Libyan rebels are capturing key towns to the south and west of Tripoli and trying to cut off supply routes to the capital in their bid to force Mr. Gadhafi from power.

On Tuesday, the French News Agency quoted the Transitional National Council envoy, Mansur Saif Al-Nasr, as saying opposition fighters had entered a “decisive phase” and could soon liberate all of southern Libya.

The rebels say they control most of Zawiya, a strategic town 50 kilometers west of Mr. Gadhafi's power base in Tripoli. Rebel fighters entered Zawiya Saturday in their closest approach to the capital since the early weeks of the uprising.

Pro-Gadhafi forces exchanged fire with rebel fighters in Zawiya Monday, trying to push them back from the town center.

Rebel spokesmen say their fighters also captured the towns of Surman, 60 kilometers west of Tripoli, and Gharyan, 80 kilometers south of the capital. Their claims could not be independently verified.

Control of Zawiya, Surman and Gharyan would allow the rebels to cut off Tripoli from a key highway to the south and another leading west to Tunisia.

Also Monday, a senior Libyan Interior Ministry official flew to Egypt with nine family members in what appears to be another defection from Mr. Gadhafi's government.

Nassr al-Mabrouk Abdullah and his relatives arrived in Cairo on a private jet from the Tunisian resort island of Djerba. Abdullah is believed to be a deputy interior minister. He entered Egypt on a tourist visa and did not meet any representatives of Mr. Gadhafi's embassy in Cairo.

Western news agencies quote sources in Djerba as saying Mr. Gadhafi's aides met Libyan rebels at a local hotel on Sunday. U.N. Secretary-General Ban Ki-moon's Libya envoy Abdul Ilah al-Khatib arrived in Tunisia Monday to join the talks between the two sides.

In an audio message broadcast on Libyan state television Monday, Mr. Gadhafi urged his people to fight to “to liberate Libya” from rebels who began their uprising in February to end his 42-year rule. He called the rebels “traitors” and denounced NATO as a “colonizer” for staging airstrikes in support of the uprising.