United Nations, Nov 23 : UN Secretary-General Antonio Guterres has strongly condemned a deadly attack in Pakistan's northwest Khyber Pakhtunkhwa province.

The attack, launched by gunmen, targeted three passenger vehicles on Thursday, reportedly killing at least 42 people and injuring 20 others, Xinhua news agency reported.

The Secretary-General stressed that attacks against civilians are unacceptable, said Stephane Dujarric, his spokesman, at a daily briefing on Friday.

Guterres extended his deepest condolences to the families of the victims and the government of Pakistan.

He called on the Pakistani government to conduct an investigation and to ensure that those responsible are held accountable.

The Shia-dominated Parachinar area has had bloody confrontational clashes with the surrounding areas of the Sunni majority in the past.

No militant groups have claimed responsibility for the attack while the security forces have initiated a search operation to track down the attackers.

Pakistan's Federal Minister Mohsin Naqvi condemned the attack, stating that the federal government is in constant contact with the KP provincial government.

'This past week has been difficult and upsetting. We see a new incident every day and now are in constant contact with the KP authorities,' he said.

President of Pakistan Asif Ali Zardari also condemned the tragic incident and said that 'attacking innocent passengers is a cowardly and inhumane act'.

Kurram agency has witnessed violent and deadly clashes in the past over land disputes between Shia and Sunni tribes. Over the years, both tribes have engaged in conflicts, which have claimed the lives of hundreds on both sides.

Since the last conflict between the tribes, the locals were allowed to travel in only convoys as per the decision taken by the local elders.

'It can at least be established that the gunmen were aware of the movement of the convoy from Parachinar towards Peshawar and had placed themselves in hiding positions around the surrounding mountains to carry out the attack,' said a local resident of Ochut.

Thursday's attack is one of the deadliest ones in the ongoing longstanding sectarian conflict between the Shia and Sunni tribes in the Kurram district.

Earlier this month, thousands of residents gathered in Parachinar to participate in a "peace march' calling on the government to enhance the security of Kurram district's 800,000 residents, over 45 per cent of who belong to the Shia community.

/IANS