A UN independent commission to look into the 2007 assassination of former Pakistani prime minister Benazir Bhutto will begin its six-month probe on July 1, the United Nations announced here on Friday.

Secretary-general Ban Ki-moon sent a letter to Asif Ali Zardari, Pakistan's president and Bhutto's husband, informing him of the start of the commission, Ban's spokesperson Michele Montas told a regular news briefing.

The three-member commission, set up in February upon the request from the Pakistani government, was headed by Chile's UN Ambassador Heraldo Munoz and will be fact-finding in nature.

"The duty of determining criminal responsibility of the perpetrators of the assassination remains with the Pakistani authorities," Montas said.

The other members of the commission are Marzuki Darusman, Indonesian former attorney general, and Peter Fitzgerald, a veteran of the Irish National Police who has served the UN in a number of capacities including heading the initial mission of inquiry into the assassination of former Lebanese prime minister Rafik Hariri in 2005, she said.

The commission will submit its report to the secretary-general within six months of the start of its work, and Ban will share the report with the Pakistani government and submit it to the Security Council for information.

Noting that the anniversary of Bhutto's birth falls on Sunday, the secretary-general said the UN is committed to assisting Pakistan by "determining the facts and circumstances of her death," according to Montas.

Bhutto was assassinated in gunshot and suicide bombing attacks on Dec. 27, 2007 after addressing an election rally in a park in the garrison city of Rawalpindi near the capital of Islamabad.

The Pakistani government has repeatedly called on the UN to establish a commission to investigate the killing.