QUETTA: Kidnappers freed four people in northwestern Pakistan's South Waziristan tribal region on Thursday, a security official said.

The four, who were among the 10 abducted from Balochistan's Killa Saifullah district early this month, hail from the province's Quetta and Zhob districts.

The official, who requested anonymity, told Dawn that the kidnappers freed the four in South Waziristan's Zarmilan area.

"It was not entirely clear how they were set free or how their release was secured,” the official said.

Armed militants had kidnapped 10 people from Killa Saifullah on Jan 4 this year. The captors had killed an official of the Pakistan Air Force who was among the kidnapped and had freed two hostages. Three people were still in the kidnappers' custody.

Security forces had also launched operations in Zhob, Killa Saifullah, Sherani and Loralai districts of Balochistan to ensure the hostages' safe recovery.

The forces had also detained some suspects in connection with the kidnapping.

Zhob serves as a transit point for insurgents operating in Pakistan's volatile northwestern tribal belt where the army is acting to root out local and foreign militant groups.

Mounting pressure on part of the armed forces has forced a number of militants to sneak into Balochistan via Zhob. However, security in and around the district has been tightened since the launch of operation Zarb-i-Azb in North Waziristan.

Militants in the past have also kidnapped government officers and workers of non-governmental organisations in the area, most of whom were freed after payment of heavy ransoms.