( Reuters ) - The Pakistan government blamed Islamist militants for a grenade and suicide bomb attack early on Friday that killed 133 people as opposition leader Benazir Bhutto drove through masses of supporters in Karachi.
Two blasts in quick succession rocked Bhutto's motorcade as it edged through hundreds of thousands of well-wishers who had stayed up late into the night to welcome the two-time prime minister back to Pakistan after years of self-imposed exile.
There was no claim of responsibility. But police were investigating whether the bomb had links to tribal regions bordering Afghanistan which have become hotbeds of support for al Qaeda and the Taliban.
"Definitely, it is the work of the militants and terrorists," Interior Ministry spokesman Javed Iqbal Cheema said, adding it was too early to say which group was involved.
Interior Ministry Secretary Syed Kamal Shah said 133 people had been killed and 290 wounded.
"The first blast was caused by a hand grenade. The second was the suicide attack," Manzoor Mughal, a senior police official involved in the investigation, told Reuters.
"The attacker ran into the crowd and blew himself up."
Bhutto, travelling in a truck reinforced to withstand bomb attacks, was unhurt in one of the deadliest attacks in her country's history.
It was the second most deadly suicide bombing of 2007, and most deadly outside a war-zone.
Mughal said the head of the suspected bomber had been found, and it was estimated he had 15 to 20 kg of explosives strapped to his body. Typically the upward force from a blast blows off the head an attacker.
"The attacker appears to be 20-21 years old, and (had) 48-hour stubble," another investigator said. A sketch was being made and DNA samples taken.
Militants linked to al Qaeda, angered by Bhutto's support for the U.S. war on terrorism, had this week threatened to assassinate her, and officials said there were intelligence reports of plots by three separate groups.
Bhutto's husband, Asif Ali Zardari, accused Pakistani intelligence agencies of involvement, and there are many Pakistanis who shared his suspicions.
Bhutto, 54, has plenty of enemies in Pakistan with links to the country's security apparatus and jihadi groups, going back to her two stints in power more than a decade ago.
President Pervez Musharraf had given some support for Bhutto's return and the two might end up sharing power after the elections in January.
The United States has quietly encouraged their alliance to keep nuclear-armed Pakistan pro-Western and committed to fighting al Qaeda and supporting NATO's efforts to stabilise Afghanistan.
Musharraf said in a statement the attack was "a conspiracy against democracy".
The United States, other allies and neighbour India condemned the attack.
The scale of Thursday's reception for Bhutto proved she has the mass appeal no other leader can muster despite being out of power for 10 years, and out of Pakistan for eight.
Bhutto had for hours stood in the open on top of the truck, ignoring police advice to stay behind bullet proof glass, as it edged through crowds waving Pakistan People's Party flags.
Idolised by impoverished villagers, Bhutto's re-entry to the political scene was also welcomed by investors who saw her as a force for democracy and stability, who would help Pakistan keep consistent economic policies.
The Karachi share index dipped around one percent in early trade in reaction to the attack, but soon recovered to just short of life highs at 14,756.73 points by midday (0700 GMT).
The market has gained around 47 percent since the beginning of the year, despite increasing political uncertainty as army chief Musharraf entered the shakiest period since coming to power in a coup in 1999.
The attack took place shortly after midnight, more than 10 hours after Bhutto had arrived from Dubai.
About 20,000 security personnel had been deployed to protect Bhutto and the provincial governor said authorities had urged her party to wind up the procession faster because of "real threats".
Bhutto's family history has been steeped in violence.
Her father, Zulfikar Ali Bhutto, Pakistan's first popularly elected prime minister, was overthrown and hanged, while her two brothers were killed in mysterious circumstances, one gunned down in Karachi, the other found dead in his French Riviera flat.