* Witnesses see air strikes on caves in remote border area
* Army encircles area, raids nearby towns
* Clashes with militants comes amid growing political crisis
Tunisian forces launched air and ground strikes on Islamist militants near the Algerian border on Friday after fierce overnight clashes in the area, which came amid increased instability and political turmoil in the North African country.
Earlier this week, militants killed eight soldiers in the remote Mount Chaambi region, in one of the deadliest attacks on Tunisian security forces in decades.
Witnesses said on Friday they saw aircraft bombing caves in the area, where the military has been trying to track down Islamist militants since December.
"A major military operation with the participation of air and ground units began at dawn on Friday," army spokesman Taoufik Rahmouni said, adding that the group of about 15 to 20 militants were surrounded by the military.
"The army has now imposed a security ring around the area and is searching nearby towns in the region. Until now there are no casualties or arrests (in Mount Chaambi)."
Rahmouni called the group near the border a "terrorist group". It is the same site where militants launched an ambush on Monday and shot dead eight Tunisian soldiers. The gunmen then slit some of the victims' throats.
Tunisia's elected ruling party Ennahda, a moderate Islamist group, is grappling with both the rising instability and a growing protest movement organised by the secular opposition that is demanding the government's ouster.
Opposition groups are angry about the assassination of one of their leaders last week, the second in six months.
Ennahda blames Salafist militants for the assassinations and for two improvised bombs that hit Tunis in the past week, the first time the capital has suffered such attacks. No one was hurt in the blasts.
In the town of Kasserine, near Mount Chaambi, security forces raided a mosque and arrested 12 Salafists, a witness in the area said.
The border area is porous and is known for smuggling, a trade that has grown in the wake of instability since Tunisians toppled autocrat Zine al-Abidine Ben Ali in 2011.
The interior ministry said on Friday its forces had also arrested a Salafist militant who had been preparing explosives in the town of Manzel Bourguiba, 50 km (30 miles) north of the capital.
Local media said the man was captured when he blew off his hand experimenting with explosives. He was taken to a nearby hospital.