The Libyan National Army led by Khalifa Haftar on Sunday carried out its first air strikes on the southern part of Tripoli since announcing last week that he was launching an offensive on the capital. "The air force took part for the first time in the military operations," said LNA spokesman Ahmed Mesmari. "It conducted a very successful operation to secure the airport road (to city center)," he added. The head of the Government of National Accord (GNA), Fayez al-Sarraj, who is based in Tripoli, accused Haftar of "betraying" him. "He will find nothing but strength and firmness," Sarraj said Saturday in televised comments. Forces backing Sarraj announced a counteroffensive on Sunday to defend the capital. The UN mission to Libya (UNSMIL) called for a truce for two hours in southern Tripoli to evacuate civilians and wounded, it said in a statement without giving details. But the true was not observed by evening, one UN official said. In another sign of the situation worsening on the ground, a contingent of US forces supporting the US Africa Command evacuated Libya for security reasons, a US statement said. "The security realities on the ground in Libya are growing increasingly complex and unpredictable," said Marine Corps Gen. Thomas Waldhauser, the head of US Africa Command. "Even with an adjustment of the force, we will continue to remain agile in support of existing US strategy." UN-sponsored talks due to start next week are designed to set a time frame for possible elections in Libya. The UN envoy for Libya, Ghassan Salame, said the United Nations is determined to hold the planned conference.