Cairo, July 28 -- The battle between rival militias for control of the Libyan capital raged amid increased fighting over the past the past 24 hours, officials said Saturday, with both sides relying heavily on airpower to make progress in the stalemated conflict.

Forces loyal to Khalifa Hifter, a veteran army officer based in the country's east, began an offensive to capture Tripoli in early April.

Hifter's self-styled Libyan National Army has been advancing into the city's southern outskirts, clashing with an array of militias loosely affiliated with the U.N.-recognized government based in the capital.

Libyan officials, who spoke on condition of anonymity because they were not authorized to brief reporters, said Hifter's LNA launched a...