Libya's Islamic State affiliate seized a civilian air base in the central city of Sirte, a militia spokesman and an ISIS statement said Friday, in the terror group’s latest attempt to exploit Libya's lingering chaos.

The takeover of the al-Qardabiya air base occurred when a militia dispatched to battle the Islamic militants, who already control of much of Sirte, withdrew. According to Mohammed al-Shamia, spokesman for the so-called 166 Battalion militia, his force retreated after calls for reinforcements from Tripoli went unheeded.

Most of Sirte-- the hometown of former leader Muammar Gaddafi-- fell to ISIS last week, the BBC reported.

An ISIS affiliate’s statement said the militant group seized the air base along with Gadhafi-era Great Man Made River water project.

The irrigation project—also the world's largest—supplies fresh water to Libyan cities and served as base for the opposition Battalion 166, which has now fled the area.

Nearly four years after the ouster of longtime dictator Moammar Gadhafi, Libya is consumed by chaos, with various militias fighting for power. The country's elected parliament and government were forced to relocate outside the capital to the far eastern cities of Tobruk and Bayda after militias linked to Islamist factions took over Tripoli last year.

The 166 Battalion militia answers to the umbrella group of Islamist-linked militias that control the capital, Tripoli. The Tripoli-based factions and militias have so far been hesitant to get into armed confrontation with the Islamic State affiliate — which has issued several statements describing them as "infidels" and urging their fighters to defect.

In the last seven months, IS has set up checkpoints and established a presence in cities across Libya, starting with the port of Darnah, the first city outside Iraq and Syria to fall to the extremist group.

ISIS militants have captured and beheaded dozens of Christian laborers and migrants, including Egyptians and Ethiopians. They have attacked oil fields while trying to expand their territory to the east of Sirte but were repelled by local fighters.

In January, an ISIS-affiliated group bombed the Corinthia Hotel in Tripoli, killing 10 people.

Air strikes against ISIS positions have been conducted by the Egyptian air force and by Libya's internationally-recognized government.

The Associated Press contributed to this report.