TRIPOLI (Reuters) - Forces allied to Libya’s internationally recognized government on Wednesday seized the town of Gharyan south of Tripoli, home to the main supply base of eastern forces attacking the capital, witnesses and Tripoli officials said.

The takeover of Gharyan by Tripoli forces is a major blow to the eastern-based Libya National Army (LNA) led by Khalifa Haftar, which on April 4 started an offensive to take Tripoli from the internationally recognized administration.

The offensive has not advanced beyond Tripoli’s southern suburbs, and the frontline had not changed significantly for weeks.

Gharyan was until Wednesday the main forward base for the LNA where troops, weapons and ammunition arrived from the East. The LNA began its Tripoli campaign here.

Forces allied to the Tripoli government, backed by air strikes, stormed the town, some 90 km (56 miles) south of Tripoli, in the morning in a surprise attack, witnesses said.

They took the central operations room of the LNA, which by evening had left the town, they added. Gharyan is also home to field hospitals and there is a helicopter base outside the town.

The Tripoli-based Presidential Council in charge of the government said in a statement Gharyan had been fully “liberated”.

One of its members, Mohammed al-Ammari, warned in a separate statement against any revenge attacks.

The LNA still holds the town of Tarhouna southeast of Tripoli, its second main position in the campaign.

“This is a game changer,” said Tarek Megerisi, a policy fellow with the North Africa and Middle East program at the European Council on Foreign Relations.

“If Haftar can’t retake it quickly (which is doubtful) Tarhouna and the remaining LNA units will be more isolated, under resourced and with lower morale,” he said.

There was no immediate comment from the LNA, whose spokesman Ahmed Mismari had hours earlier said that an attack by Tripoli forces had been repelled.

Haftar and his backers say they are trying to free the capital from militias which they blame for destabilizing Libya since the fall of Muammar Gaddafi in a NATO-backed uprising in 2011.

Haftar’s critics accuse him of trying to seize power through force and deepening a conflict between factions based in the east and west of the sprawling North African country.

Haftar’s offensive has upended United Nations-led plans to stabilize Libya after years of conflict that have left the oil-rich nation divided and caused living standards to plummet.

The conflict risks disrupting oil production, creating a vacuum exploited by militants and prompting more migrants to leave for Italy by boat.