At least 38 people were killed and 29 were injured after gunmen opened fire on passenger vehicles in a tribal area in northwestern Pakistan on Thursday, reported Reuters quoting the chief secretary of the Khyber Pakhtunkhwa province, Nadeem Aslam Chaudhry.

The attack, which took place in the Kurram tribal district, resulted in several fatalities, including a woman and a child, Chaudhry stated, adding that it is a significant tragedy and the death toll is expected to increase.

Tensions have existed for decades between armed Shia and Sunni Muslims over a land dispute in the tribal area that borders Afghanistan. No group claimed responsibility for the incident.

"There were two convoys of passenger vehicles, one carrying passengers from Peshawar to Parachinar and another from Parachinar to Peshawar, when armed men opened fire on them," a local resident of Parachinar, Ziarat Hussain told Reuters by telephone, adding that his relatives were travelling from Peshawar in convoy.

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President Asif Ali Zardari, in a statement, strongly condemned the attack on passenger vehicles.

Earlier on Wednesday, 12 security personnel were killed in a suicide attack on a joint check post in Pakistan's Khyber Pakhtunkhwa province. The attacker rammed a vehicle filled with explosives into the checkpost. During this, six attackers were also killed.

The army did not say who was behind the attack but an Islamist group Hafiz Gul Bahadur claimed responsibility for it. The attack came after the federal apex committee approved a massive military operation against Balochistan insurgents.

Prime Minister Shahbaz Sharif chaired the meeting which was attended by federal ministers, chief ministers, Army Chief General Syed Asim Munir and senior government officials.