By Ayman al-Warfalli

BENGHAZI, Libya (Reuters) - The dominant armed force in the east Libyan city of Benghazi said on Thursday it had taken control of one the last holdouts of Islamist-led militias, amid clashes in which at least 18 troops were killed, according to medical officials.

The self-styled Libyan National Army (LNA), whose commander, Khalifa Haftar, is a figurehead for factions aligned with an eastern-based government, has been fighting Islamist militants and other militias in Benghazi for more than two years.

Fighting resumed this week in the southwestern district of Ganfouda, and in nearby Guwarsha, the area in which the LNA said it had now flushed out the opposing forces.

"The forces of LNA have liberated Guwarsha and our forces found 15 bodies belonging to terrorist groups," military spokesman Ahmed al-Mismari told Reuters.

A video circulating on social media showed LNA special forces field commander Wanis Boukhamada shouting into a radio: "Repeat, repeat, the main road of Guwarsha district Shajar Street has fallen! ... God is great."

Libya slid into political turmoil and conflict after Muammar Gaddafi was toppled in an uprising five years ago. In 2014, rival parliaments and governments were set up in Tripoli and eastern Libya, both backed by loose alliances of armed groups. The eastern government, supported by the LNA, is opposed to a U.N.-backed government that arrived in Tripoli in March.

Clashes were continuing on Thursday around Ganfouda, where the LNA has besieged fighters from the Benghazi Revolutionaries Shura Council (BRSC), the main group fighting it.

The LNA also conducted air strikes in Ganfouda and another district, Sabri, a military official said.

At least 18 LNA soldiers were killed and 54 wounded in the fighting, medical officials said. Four of the dead were killed in a mine explosion in Guwarsha, they said.

A car bomb exploded near a building captured by the LNA in Ganfouda, though the number of casualties was not immediately clear, security and medical officials said.

The BRSC claimed responsibility for the bombing, according to a statement posted from a Twitter account close to the group.

The LNA also has a presence in parts of southern Libya.

(Writing by Aidan Lewis; Editing by Catherine Evans)