Pakistani officials differed on the exact location of the incident, saying it either took place in Upper Kurram or Upper Orakzai.

巴基斯坦官员就事件发生的确切位置上说法不一，说它要么发生在上古勒姆或在奥拉克赛。

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Hangu is a Sunni majority town, but is located on the main route to the mainly Shia Kurram region.

BBC: Pakistan bomb: 21 die in Hangu Shia suicide attack

Two polio vaccination workers have been killed in a landmine blast in the Kurram tribal region of north-west Pakistan, officials say.

BBC: Polio workers in Pakistan

Correspondents say Sunni militants may have planted the mine - the upper Kurram area is dominated by Shias who do not oppose anti-polio efforts.

BBC: Polio workers in Pakistan