United Nations, July 15 - A three-member UN commission appointed to probe the 'facts and circumstances' of the assassination of former Pakistan prime minister Benazir Bhutto will soon start investigations but will have limited mandate, an official said.

The fact-finding body will arrive in Pakistan in the next few days to begin investigations on the ground.

However, its mandate does not include undertaking criminal investigations or prosecuting the perpetrators, which are the sole responsibility of the Pakistani government, a spokesperson for the office of the UN secretary general told reporters here.

It is not clear whether 'facts and circumstances' means assigning blame.

Chile's UN Ambassador Heraldo Munoz will head the commission that was constituted July 1. The other two members are Indonesia's former attorney general Marzuki Darusman and Peter Fitzgerald, a retired officer of Ireland's police force.

The first woman prime minister of a Muslim country, Bhutto went on self-imposed exile in Dubai in 1998 but returned in October 2007 to campaign for the Pakistan Peoples Party (PPP) in parliamentary and provincial elections. She was killed in a gun and bomb attack at a rally in the garrison town of Rawalpindi Dec 27, 2007.

Investigations carried out by then president Pervez Musharraf's government blamed Baitullah Mehsud, a Pakistani Taliban commander who operates in the lawless tribal areas of northwest region.