At least four Tunisian police officers have been killed in a pre-dawn attack by a group linked to al-Qaeda, officials have said.

Tunisia's Interior Ministry said on Wednesday that about 20 fighters attacked a checkpoint in the central Kasserine region before killing the police officers and stealing their weapons.

"A group of 20 terrorists attacked a patrol of the National Guard," Mohamed Ali Aroui, the ministry spokesman said.

"The gunmen opened fire at a police car, killing the four policemen, and fled with their weapons." 

Prime Minister Habib Essid called it a "cowardly terrorist attack" and said authorities would respond harshly.

"We will chase the terrorists, the assassins, into their hideouts in order to exterminate them and clean up the country," he told reporters in Tunis.

There was no immediate claim of responsibility but Okba Ibn Nafaa, a small brigade of fighters operating along the Algerian border was blamed.

The group claimed a July 2014 attack that killed 15 soldiers in the Chaambi region in what authorities said was one of the deadliest assaults in the army's history.

Since April last year, thousands of soldiers have been deployed to drive out groups from the Chaambi region that borders Algeria.

According to authorities, fighters took refuge in Chaambi after fleeing French military intervention in Mali last year.

Tunisia recently completed its transition to democracy after the 2011 uprising against Zine El-Abidine Ben Ali, but security remains a key worry due to the emergence of armed groups.

Source: Agencies