At least 33 people were killed in northwestern Pakistan on Saturday.

The Pakistani Army says Afghanistan-based militants staged a cross-border raid on paramilitary checkposts in the district of Chitral, but Afghan officials deny the militants came from their side of the border.

In a statement, the Pakistani military said the 200 to 300 militants involved in the attack came from Afghanistan’s Kunar and Nuristan provinces and were organized by Maulvi Faqir Muhammad, a deputy leader of the Pakistani Taliban, and the radical cleric Maulanah Fazlullah, more commonly known as ‘Radio Mullah.’

In 2007, FRONTLINE correspondent David Montero traveled to northern Pakistan’s Swat valley to explore how the once-peaceful area had become a safe haven for militants and interviewed the media-shy cleric, who had gained fame for his daily FM radio sermons. Back then, Fazlullah was the leader of  of the Tehreek-e-Nafaz-e-Shariat-e-Mohammadi (TNSM), a Swat-based fundamentalist group allied with the Pakistani Taliban that sought to implement Sharia law in the country.

TNSM gained local support by exploiting grievances with Swat’s justice system, pledging to bring more speedy justice through Sharia law. But Fazlullah and his forces — made up of foreign fighters and local insurgents — lost support after a violent campaign in the valley in which they targeted the Pakistani military, political leaders, police officers and even the local population, beheaded those they deemed un-Islamic, bombed girls’ schools and carried out suicide attacks.  In his radio sermons, Fazlullah denounced “immoral” activities like music and dancing, and announced the names of alleged criminals to target.

The ‘Radio Mullah’ was thought to have fled to Nuristan after a 2009 campaign by the Pakistani military drove the TNSM and Pakistani Taliban from the area.  Swat is still recovering from the violence.  Despite reports that he may have been critically injured or killed, Fazlullah appeared alive and well in a 40-minute video obtained by Newsweek in January, threatening the Pakistani military and its supporters.

The Pakistani Army’s claim that Fazlullah and his supporters have regrouped in Afghanistan — with the support of local authorities — will likely further strain Pakistan’s relations with Afghanistan and the U.S.  The attack in Chitral is the latest in a series of cross-border raids that Pakistan blamed on the “scanty presence” of NATO and Afghan forces along the border.

Saturday’s attack may also renew Pakistani fears that Fazlullah will continue to target the country.