Renewed fighting has broken out in Benghazi, a day after the retired general Khalifa Haftar vowed to "liberate" the city from what he called terrorists.

Sources told Al Jazeera that gunfire and explosions were heard early on Wednesday and that aircraft belonging to the general's forces were striking targets around the eastern city.

Witnesses said tanks and jets had targeted the February 17 Martyrs Brigade, a rival to Haftar's forces which operates in parts of Benghazi.

The group is part of the Shura Council of Benghazi Revolutionaries, a military coalition allied with the al-Qaeda-linked armed group Ansar al-Sharia and control most of the city.

In a speech broadcast late Tuesday, Haftar said his forces would liberate the city.

Al Jazeera's Mahmood Abdulwahid, reporting from Tripoli, said that the offensive launched by Haftar's forces was responded to by a counter-offensive by the militia groups.

"The situation is very tense [and] the battle is going on around the Benina airport, located just outside of Benghazi," he said.

The oil-rich North African nation has been gripped by turmoil since the 2011 uprising against long-time leader Muammar Gaddafi.

A parliament, elected in June, is recognised by the international community but contested by the militia controlling most of Tripoli, where an alliance of armed groups hold sway, and by other armed groups who dominate Benghazi.

The prime minister Abdullah al-Thinni and his elected parliament have moved to the far eastern city of Tobruk after militias opposed to its rule took over the capital and set up their own administration and cabinet.

Haftar launched an offensive dubbed "Operation Dignity" against militias in Benghazi in May, but his forces were repelled from the city in July.

At least 22 people, including soldiers, have been killed in violence in Benghazi in the past 48 hours, the AFP news agency reported. citing military and hospital sources.

Source: Al Jazeera and agencies