Ansar al-Sharia, the Islamist militant group blamed for the 2012 raid on the US consulate in Benghazi, is celebrating gains in the east of Libya after taking control of a series of military bases. The group’s victories are sparking fears that Benghazi’s air force base could be overrun.

The base is located 15 kilometres to the east of the city next to Benghazi’s civilian airport and has been launching daily bombing raids on Ansar al-Sharia bases across the city.

“The air base is under serious threat. It could fall into the hands of the Islamists after the Special Forces lost their base,” says Osama Buera, a spokesman for a military group allied with Khalifa Haftar, the retired general currently leading a war against Islamists in Libya’s east.

Haftar started his assault in May without authorisation from Libya’s central government and claimed several victories in the early days of the conflict. Over recent weeks, however, the tide has turned despite frequent bombardments from air force units supporting Haftar’s campaign.

Benghazi’s Special Forces pledged allegiance to Haftar in May and has a reputation for having the best-trained fighters in the country, but its Bu Attni base was overrun by a coalition of Islamist militias on 29 July after sustained fighting with Grad rockets and mortars. While the air force bombers provided support to the fighters defending the base, no other anti-Islamist ground troops came to their aid.

“They were fighting alone, no [other] forces related to Haftar stood by their side,” says Buera.

Ansar al-Sharia claims to have siezed a number of other bases from the military in recent weeks, including bases 21 and 319, as well as the base named 2 March. Supporters of Haftar’s campaign say some of these bases were already abandoned by the military before the Islamists took control.

Since the loss of the Bu Attni Special Forces base, the fighters located there have moved to the town of Ar Rajmah, 20km east of Benghazi, where Haftar is amassing the main body of his troops as he waits for permission from Libya’s newly elected House of Representatives (HoR) to take on Ansar al-Sharia and its allies in a ground assault.

The new legislature held its first session earlier on 4 August and it is not yet clear whether it will officially sanction Haftar’s war with Ansar al-Sharia, although it is likely to be more supportive than the previous transitionary government, the General National Congress (GNC). Haftar accused the GNC of supporting terrorism in Libya, and ignored its orders to stop his military operations in the east.

While most of Haftar’s ground troops idle, Benghazi’s air force has been working long hours.

“Every day there is an attack. People feel happy when they hear the sound of the planes,” says Emad Salem Bkkar, a Haftar supporter who lives in Benghazi’s Shipna district.

“The clap of every bomb sounds now like music for us. The people [in my area] want anything [that] can kill anyone in Ansar al-Sharia.”

Fighting between militia factions in Tripoli and Benghazi has killed hundreds and displaced thousands over recent weeks. On 6 August, Amnesty International said indiscriminate shelling by militias in built up areas in the two cities amounted to war crimes and there are growing concerns about a mounting humanitarian crisis as the country becomes increasingly chaotic.

“In the city [of Benghazi] most banks are closed and soon there will be a shortage of food and medical supplies,” says Buera.

A UN delegation held talks in Tripoli on 8 August in an attempt to negotiate a ceasefire between the groups fighting in the country’s two biggest cities, but so far there has been no sign of any progress.

Ahead of the meetings the UN released a statement saying: “UNSMIL is working closely with the international community in a joint effort to achieve a durable and sustainable ceasefire.” The UN has also voiced concerns about torture and attacks on civilians, warning that both are war crimes under international law.