Updated

The U.N. Secretary General has expressed deep concern about the recent escalation of violence in Libya, including recent airstrikes on a military air base that until this week was Tripoli's only functioning airport.

In a statement Wednesday, Ban Ki-moon called on all sides to end the fighting. His envoy, Bernardino Leon, asked the head of the internationally-recognized government, Abdullah al-Thinni, to stop airstrikes on the Matiga air base, held by Islamist militias who with their allies control the capital.

Al-Thinni described the strikes by Libya's air force as "preventive" against militias who were planning attacks against his government.

Ban also said violations of U.N. premises in Tripoli can't be tolerated. On Monday, dozens of protesters gathered just outside the gates of the U.N. office, denouncing Leon and urging his departure.