The bloodbath at Benazir Bhutto's homecoming has pushed nuclear-armed Pakistan to crisis point, both politically and in its US-backed battle against Al-Qaeda and the Taliban, analysts said.
Her carnage-strewn return from exile deepened the faultlines that threaten the Islamic republic of 160 million people, which has lurched from one existential threat to another in its six decades of independence.
The blasts could move Bhutto closer to a power-sharing deal with key US ally President Pervez Musharraf, which western nations have pushed as a solution to the militancy seeping from Pakistan across the world.
Bhutto pledged to take on Islamic extremism in a defiant speech after the suicide and grenade attack on her homecoming parade that killed nearly 140 people, adding that she did not blame the "state or the government."
But fingerpointing over the alleged involvement of former officials and spy agencies in the wake of the attack could still scupper a pact that would likely bring a measure of stability ahead of general elections in January.
Military ruler Musharraf meanwhile could yet break his promise to quit as army chief by November, eight years after the coup that brought him to power, if the Supreme Court overturns his recent victory in a presidential election.
His popularity has slumped since he tried to sack the court's chief justice in March -- while Islamic militants have paid him back for a bloody raid on the Red Mosque in Islamabad in July with 22 suicide bombings since then.
The militants too are at a crucial juncture, having taken control of the tribal belt bordering Afghanistan but fearing the move to civilian, democratic rule will foil their bid to spread Taliban-style Islamic sharia law.
"We are heading towards a major crisis," Moonis Ahmar, professor of international relations at Karachi University, told AFP.
Analysts said Pakistan itself now faces the choice Bhutto did when she returned home -- face a mortal risk at the hands of militants, or give in to extremists.
If the country chooses to go head-on at the threat, then political consensus will be vital, they added.
"Bhutto and Musharraf will be more vulnerable if they stand divided and pursue power separately," said Rasul Baksh Rais, a political science professor at the Lahore University of Management Sciences.
"We have to put the political house in order, because as long as we have political contests and rivalries we may not be able to sustain our fight against terrorism," he added.
A key step will be severing the militants' umbilical cord: their links to a network of rogue or former army and intelligence officials who offer financial and logistical support, analysts said.
Bhutto implicated such officials in the immediate aftermath of Thursday's Karachi attacks, while Musharraf admitted several months ago that some former spies were still backing the Islamists.
"Some of the rogue elements in the establishment who feel there is pressure on them for democracy want to create insecurity to deny mainstream political parties space," Karachi University's Ahmar added.
"They tried to kill two birds with one stone in Karachi."
Islamic militants have previously tried to kill Musharraf -- marked for death by Osama bin Laden in a recent video -- at least three times, including a bid to shoot down his plane during the Red Mosque crisis.
The election process itself, marred by violence at the best of times in ethnically and politically divided Pakistan, could now be at risk amid the current wave of violence, analysts said.
"Perhaps the political parties will have to redefine their strategy to conduct electioneering in the face of this very serious threat," said political analyst Shafqat Mahmood.
But a strategy to combat radicalism, especially in the tribal areas where it is mixed with Pashtun nationalism, is an even greater challenge -- with the use of force proving increasingly counterproductive.
Around 250 people, believed to include some civilians, died in fighting along the Afghan border earlier this month in battles between militants and the army.
"Unfortunately General Musharraf and Bhutto are seen by militants as adversaries, and the option of dialogue goes out of window. The only option left is use of force, which is not going to resolve the problem," Mahmood said.