Pakistan's military said it killed 34 militants Wednesday in air strikes on a tribal region near the Afghan border as part of a major offensive against insurgents that began last year.

The Taliban and Lashkar-e-Islam militant groups are based in Khyber, one of seven autonomous tribal districts along Pakistan's western border, which became a hideout for Islamist militants following the US-led invasion of neighbouring Afghanistan in 2001.

"In precise aerial strikes in Tirah, Khyber region, 34 terrorists were killed today," the military said in a statement.

The military began its latest offensive in Khyber in October 2014, four months after a similar operation in the North Waziristan district which was triggered by a bloody Taliban attack on Karachi airport that sank faltering peace talks.

Both conflict zones are off-limits to journalists, making it difficult to verify the number and identity of those killed.

Rights activists are wary of the death tolls given by the military and say many women and children have also died.

Air strikes, artillery, mortars and ground troops have all been used to take back territory.

Also Wednesday a polio worker was shot dead in the tribal district of Bajaur, underscoring the continuing violence against vaccination teams as Pakistan tries to eradicate the crippling childhood disease that is endemic in only two other countries -- Nigeria and Afghanistan.

"A polio worker was shot dead while another sustained injuries when they were fired upon while administering polio drops in Khamangra neighbourhood of Nawagai area in Bajaur tribal district," local administration official Fayaz-ul-Haq Sherpao told AFP.

The attack was confirmed by another senior administration official, Sohail Ahmed Khan. It brings to 78 the number killed in attacks on immunisation teams since December 2012.

Taliban militants have long claimed the polio vaccination drive is a front for espionage or a conspiracy to sterilise Muslims. They intensified their strikes after the CIA recruited a doctor to carry out a fake immunisation drive to help track down Al Qaeda chief Osama Bin Laden.

Last year the number of polio cases recorded in Pakistan soared to 306, the highest in 14 years.