Four Tunisian police forces have lost their lives in a “terrorist attack” in a western mountainous region near the Algerian border, the Tunisian government says.

“On February 18, following a terrorist attack in Boulaaba in the governorate of Kasserine, four heroes of the National Guard were martyred,” the Tunisian Interior Ministry said in statement released on Wednesday, without giving more details.

Boulaaba is situated at the foot of Mount Chaambi on a range bordering Algeria. The city is home to Tunisia’s main militant group, the al-Qaeda-linked Phalange Okba Ibn Nafaa, which was blamed for an attack in July last year that claimed the lives of 15 Tunisian soldiers.

Since late 2012, Tunisian troops have been battling dozens of militants hiding out in the areas near the Mount Chaambi. However, they have so far been unsuccessful in uprooting them.

More than 20 security personnel were reportedly killed in Tunisia in 2013 in what the government described as terrorism-related incidents. Two opposition politicians were also assassinated in the same year in separate attacks.

The new government of Prime Minister Habib Essid is faced with the challenge of terrorist attacks, which intensified after the 2011 revolution against Western-backed ruler Zine El Abidine Ben Ali.