Two airstrikes in Libya’s capital city of Tripoli killed 15 fighters and injured 20 other people, according to an official of the Islamist-allied Misrata militia cited in media reports Saturday. The airplanes carrying out the strikes could not be identified, the Associated Press reported. The planes fired at the Interior Ministry building in the capital, as well as other positions held by the militia. A warehouse also was hit, leading to a fire.

The latest attack is similar to one earlier this week, when unidentified airplanes also attacked Tripoli and killed six people over two days. No group has claimed responsibility for the attacks yet.

This month, Tripoli’s international airport was the scene of clashes that killed 22 people.

Libya has been engulfed in constant violence since 2011, when a revolution began against the country’s longtime ruler, Moammar Gadhafi. During this period of almost-constant clashes, the national economy has taken a major hit, with its crude-oil production fluctuating wildly.

The United Nations condemned violence in the region last week, as it appointed Bernardino Leon as the new special representative of the U.N. secretary-general for Libya and the head of the U.N. Support Mission in Libya in an attempt to reduce the violence there.