KHAR, Pakistan - Two women school teachers were killed Wednesday when armed Islamist militants ambushed their car in Pakistan's troubled tribal region bordering Afghanistan, local officials said.

The women were travelling from the school they taught at in Khar - the main town in the northwestern tribal district of Bajaur - when insurgents bearing automatic weapons sprayed the vehicle with bullets.

"Two women teachers were killed and two men were injured in the firing by militants," administration official Adalat Khan told AFP. Tribal police confirmed the incident.

Islamist insurgents who oppose the education of girls have bombed and destroyed hundreds of northwestern schools in recent years.

Militants have recently stepped up activity in Bajaur, one of Pakistan's seven semi-autonomous tribal districts straddling the Afghan border, which are considered a stronghold of Taliban and Al-Qaeda-linked extremists.

Officials warned that the Taliban and their allies were increasing attacks in areas such as Bajaur to divert attention away from South Waziristan, the Taliban bastion where the military is conducting a major ground offensive.

A similar military assault in Bajaur starting in August 2008 ended in February with the army claiming success. But militant violence continues to rock the area.

Hundreds of extremists are believed to have fled into Pakistan's semi-autonomous tribal areas to carve out safe havens after the ouster of Afghanistan's hardline Taliban regime in a US-led invasion in 2001.