A Libyan official and residents say heavy clashes are slowly nearing the center of Libya's capital, Tripoli, as forces loyal to the military commander Khalifa Hifter battle to seize power.

Hifter's self-styled Libyan National Army launched an offensive last month to take Tripoli from militias loosely allied with a U.N.-supported government.

Saraj al-Majbri, an aid to the LNA's chief of staff, said Monday its forces had made gains in the area of Salah al-Deen, a few kilometers from the city center.

Two residents said heavy fighting was taking place along a strategic road linking the capital with its international airport, which has not been functional since 2014.

They spoke on condition of anonymity for their safety.

The fighting has reportedly killed at least 562 people, including combatants and civilians.