CBS News' Farhan Bokhari in Islamabad contributed to this report.
A notorious Pakistani tribal warlord with strong links to al Qaeda and the Taliban is at the center of investigation Sunday night following a brutal suicide attack in Islamabad which, according to some accounts, killed up to 19 people, mostly policemen.
Baitullah Mehsud, the tribal warlord who has led an anti-government insurgency in the rugged mountainous region of Waziristan, close to the Afghan border, was being investigated for the attack, a senior Pakistani security official told CBS News on condition of anonymity.
In May of this year, the Pakistani military arranged a visit to a remote town in Waziristan for Western news organizations (including CBS), where debris of a suicide training school was shown to journalists. At the time, Pakistani officials claimed that the school, which operated in a leather production factory, housed children as young as twelve who were trained to carry out suicide attacks.
On Sunday, speaking about an hour after the attack in central Islamabad, the Pakistani security official said authorities had found "some clues which give a strong possibility of a Waziristan connection, a Baitullah Mehsud connection." He refused to discuss further details of the evidence that was under investigation.
Anger over the Waziristan assault is still strong, reports CBS News Correspondent Richard Roth, and some believe the latest suicide bombing was a revenge attack.
But Pakistanis bent on violence have a catalog of complaints against the government. It includes the country's pledged partnership with America on anti-terror efforts along the border with Afghanistan and cooperation in the hunt for Osama Bin Laden.
The blast occurred in a kiosk in front of the police station, which is also near Islamabad's Melody Market, said Naeem Iqbal, a police spokesman. Television footage showed wounded security forces being taken away and ambulances rushing to the area.
Just moments before the explosion, an Associated Press reporter passed by the scene and saw more than 20 security forces gathered in the vicinity.
After the blast, a traffic intersection in the area was splattered with blood. Body parts were scattered as far as 50 yards from the scene. Shattered glass also covered the area, which police cordoned off.
The casualties were mostly policemen and officers stationed near a congregation of Islamists which had been called to commemorate the first anniversary of last summer's attack by the Pakistani military on a Taliban-style mosque in the center of the Pakistani capital.
The explosion also came following recent threats of revenge from militants in Pakistan angered by a paramilitary operation against insurgents in the tribal northwest.
Since Saturday, Pakistani authorities had tightened security and regularly checked cars, buses and trucks driving into the city.
After Sunday night's attack, Rehman Malik, adviser on interior affairs to the Pakistani prime minister, said the death of at least eight people had been confirmed. Talking to reporters after visiting the scene of the attack, Malik said, "There are at least 23 other people who are injured."
However, Pakistani broadcaster GEO TV quoted hospital sources saying at least nineteen people were killed in the attack.
Western diplomats warned that the attack was a powerful reminder of uncertain security conditions faced by Pakistan, almost five months after a new government consisting of political parties opposed to pro-U.S. president Pervez Musharraf came to power.
Last week, after a visit to Pakistan, U.S. assistant secretary of state for central and south Asia Richard Boucher publicly urged the newly-elected government leaders to set aside their continued opposition to Musharraf and instead focus on key issues, including security and an increasingly moribund economy.
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