(Adds details on previous attack, background on groups)
TUNIS, July 2 (Reuters) - Four Tunisian soldiers were killed in a landmine blast during an operation against Islamist militants in the north of the country, TAP state news agency reported on Wednesday.
Tunisian troops are battling militants from the hardline Islamist group Ansar al-Sharia and other al Qaeda-linked fighters, especially since April when they began a new offensive on militant hideouts in the Chaambi mountains bordering Algeria.
Six other security force members were wounded in a mine blast a day earlier in the same mountainous region as Wednesday's attack near Kef.
Since its 2011 uprising that ousted autocrat Zine El-Abidine Ben Ali and opened democracy, Tunisia has struggled with radical Islamist movements who promote a hardline interpretation of Islam in one of the Arab world's most secular countries.
After the killing of two opposition leaders by Islamist militants last year, the small North African state declared Ansar al-Sharia a terrorist group. Washington also brands the movement a foreign terrorist organisation.
Thousands of troops were deployed to the remote Chaambi mountain area in April to flush out militants. Ansar al-Sharia has clashed repeatedly with security forces, and al Qaeda's regional wing, al Qaeda in the Islamic Maghreb, has also claimed attacks in Tunisia. (Reporting by Tarek Amara; Writing by Patrick Markey; Editing by Janet Lawrence)