Pakistan's military said it had killed 25 militants in air strikes along its restive border with Afghanistan on Thursday as part of a major offensive to clear Taliban and Al-Qaeda strongholds that began last year.

The strikes were carried out close to the Datta Khel area of the North Waziristan tribal region, the main bastion of Islamist militants who rose up against the state in 2004.

"Twenty-five terrorists were killed in precise aerial strikes today," the military said in a brief statement.

The conflict zone is remote and off-limits to journalists, making it difficult to verify the army's claims, including the number and identity of those killed.

Overall levels of militancy-linked violence have dropped dramatically this year, with 2015 on course for the fewest deaths among civilian and security forces since 2007 -- the year the Pakistani Taliban umbrella group was formed.

Pakistan's Islamist insurgency began after the US-led invasion of neighbouring Afghanistan in 2001 which led to a spillover of militants across the border and a surge in recruitment for Pakistani militant groups.

Pakistan's relative success in fighting militancy this year stands in marked contrast to neighbouring Afghanistan, which is facing record numbers of civilian casualties following the withdrawal of NATO combat troops at the end of 2014.

The brief capture of the northern Afghan city of Kunduz this week dealt a stinging blow to the country's NATO-trained military and highlighted the insurgency's potential to expand beyond its rural strongholds.