Two policemen were killed in a clash with a "terrorist" group west of the Tunisian capital on Thursday, the interior ministry said.

"Two National Guard agents were killed and a third was wounded in a confrontation with an armed terrorist group" in the Beja region, 70 kilometres (45 miles) from Tunis, it said in a statement.

The wounded man is in serious condition, a police source told AFP.

The ministry gave no details on the incident "in the interests of the smooth running of the operation" by security forces.

According to Radio Shams-FM, the police had been tipped off about an armed group operating out of a house in the area. The gunmen escaped, it said.

Islamist militancy has been on the rise in Tunisia since the 2011 revolution -- the first of the Arab Spring -- but authorities had not previously reported that armed groups were active in the Beja region.

Security forces have since last December been tracking an armed group thought to be linked to Al-Qaeda in the Chaambi mountain region along the Algerian border.

The group is linked to Tunisia's main Salafist movement, Ansar al-Sharia, charged with murdering opposition politicians Chokri Belaid and Mohamed Brahmi this year.

Ansar al-Sharia leader Saif Allah Bin Hussein, a former Al-Qaeda fighter in Afghanistan, is also accused of orchestrating a deadly attack on the US embassy in Tunis last September. He is thought to be holed up in Chaambi.

Some 15 soldiers and police have been killed in jihadist shootings or bombings in the region since the end of 2012.

Authorities have not confirmed media reports of an attack Wednesday on a post in the northwestern region of Jenduba along the border with Algeria.

No casualties were reported.