(Releads with details of fresh threat) By Simon Cameron-Moore KARACHI, Oct 23 (Reuters) - Pakistani opposition leader Benazir Bhutto received a death threat from a "friend of al Qaeda" on Tuesday, four days after 139 people were killed in an assassination attempt by one or more suicide bombers. No arrests have been made since last Friday's attack in Karachi, which government officials swiftly blamed on Islamist militants operating out of tribal areas that have become hotbeds of support for the Taliban and al Qaeda. Police were unsure whether there were two suicide bombers or one, and had yet to confirm whether the photograph released of a severed head belonged to a suicide bomber, Karachi police chief Azhar Farooqui told Reuters. The investigation hadn't singled out any particular organisation, the police chief said, but Interior Minister Aftab Ahmed Khan Sherpao said the trail led to tribal areas bordering Afghanistan. "Suicide bombers are trained in Waziristan and some other places in tribal areas. There are three groups in Waziristan. So the tracks go to tribal areas," Sherpao told independent television news channel ARYONE. A fresh threat to kill Bhutto was passed onto her lawyer, Senator Farooq Naik, by a government prosecutor on Tuesday. Written by someone who described himself as the "chief of suicide attackers" and a friend of Osama bin Laden, al Qaeda, and Pakistani jihadis, the letter said Bhutto could be stabbed, attacked in her car, or in her bedroom, Naik told Reuters. Naik said the threat should be taken seriously, even if the letter may have been written by a crank. "Benazir Bhutto doesn't want democracy to be interrupted and she is not deterred by such threats," Sherry Rehman, Pakistan People's Party (PPP) Information Secretary, told reporters. Bhutto, who came back from eight years of self-imposed exile last Thursday, has said she told General Musharraf that members of the establishment were involved in a conspiracy against her. Deputy Information Minister Tariq Azim Khan revealed the Chief Minister of Punjab province, Chaudhry Pervez Elahi, was one of the people named by Bhutto, but said such accusations hurt chances of a rapprochement. "If this trend of implicating political rivals into false cases continues, what chances for national reconciliation will there be?" Khan said. Bhutto is negotiating with Musharraf, who came to power in a coup eight years ago, over a transition to civilian-led democracy. The United States is believed to be quietly encouraging the two to work together. They are seen as progressive and pro-Western leaders who will support NATO efforts to stabilise Afghanistan and fight al Qaeda militants in nuclear-armed Pakistan. U.S. Ambassador Anne Patterson met Bhutto for around 30 minutes on Tuesday, according to PPP officials. While Bhutto has maintained a high profile, visiting victims in hospital, going to neighbourhoods where support for PPP is strong and meeting the media regularly, the government has been mostly quiet. It is unclear why government leaders have taken a lower profile given the heavy loss of life. While speculation persists that Musharraf and Bhutto could share power after elections due in January, Bhutto says such talk is premature -- particularly with the Supreme Court still to rule on whether Musharraf's own re-election by parliament earlier this month should stand, since he contested while still army chief. Whereas Musharraf's popularity is falling, the hundreds of thousands of people who came out to greet Bhutto when she returned to Karachi on Oct. 18 showed she retains grassroots support in southern Sindh province, where her party is strongest. Critics had expected allegations of corruption, an expedient amnesty granted by Musharraf, her negotiations with the general, and perceived U.S. backing would cost Bhutto support. Bhutto was expected to soon visit the town of Larkana, her ancestral home and burial place of her father, Pakistan's first popularly elected prime minister, Zulfikar Ali Bhutto. (Additional reporting by Zeeshan Haider, Asim Tanveer, Kamran Haider and Imtiaz Shah)
