LONDON, April 14 — Hours before he was scheduled to be executed last month, the Pakistani hit man made an incendiary accusation.
Speaking into a video camera at a remote desert jail, Saulat Mirza, a death-row convict from the port city of Karachi, said his orders to kill had come from Altaf Hussain, the city’s most powerful and, until recently, untouchable political leader.
“Altaf Hussain directly gave us the murder instructions,” Mr. Mirza said in footage that was broadcast on several television news channels later that evening in March.
It was enough to earn Mr. Mirza a last-minute reprieve, as the authorities investigated his claims. Mr. Hussain, for his part, called it a conspiracy to damage his image.
But in Karachi, Pakistan’s largest and most volatile city, the accusations were seen as further evidence that the political winds were violently shifting against Mr. Hussain after decades of iron-fisted dominance.
On March 11, Rangers in balaclavas raided Nine Zero, the fortified headquarters of Mr. Hussain’s party, the Muttahida Qaumi Movement, confiscating weapons and files. One political worker was killed by gunfire during the raid, and several others were taken into custody, some on murder charges.
On the political front, Mr. Hussain has come under attack from the opposition leader Imran Khan, who has started an aggressive foray into his electoral heartland. On Friday, in a symbolic challenge, Mr. Khan held a small event just a few hundred yards from Mr. Hussain’s party headquarters.
In London, the British police are continuing to press criminal investigations of Mr. Hussain and his inner circle. On April 1, a senior aide, Muhammad Anwar, was arrested on suspicion of money laundering.
Mr. Hussain, who was arrested in connection with the same case in June, underwent further questioning at a London police station on Tuesday. His bail has been extended until July.
Not long ago, any of those shocks would have caused an immediate shutdown of Karachi, a city of 20 million people where Mr. Hussain’s ability to empty the streets at an hour’s notice has long been a sign of his immense influence.
But this past month, life has largely continued as normal. Muttahida’s militant wing — organized groups of armed supporters who carry out extortion and intimidation, and are seen as the enforcers of Mr. Hussain’s authority — has melted off the streets.
The news media, which previously treated the party with caution, has aired criticism of the party. (Among those arrested was a Muttahida supporter charged with the murder of Wali Khan Babar, a prominent television journalist who was shot dead in his car in 2011.) And in the city’s political back rooms, senior Muttahida officials have begun to quietly consider the possibility of a new leader — an unthinkable idea until recently.
“The fear factor is gone,” said a senior party official who, like several others, spoke on the condition of anonymity out of fear of retribution.
But the upheaval has also brought worries of new instability in a city that is awash with armed groups. Noting that Karachi is in a “state of flux,” the newspaper Dawn warned in an editorial this month that “when the chips fall, they may not do so without considerable violence.”
The moves against Muttahida are part of a broader effort to stem a cycle of political and criminal violence that has left Karachi prone to Taliban infiltration in recent years. Militants disrupted election campaigning in 2013, leading to a crackdown that has broken several Taliban cells, according to police officials and ethnic Pashtun community leaders.
Now the authorities have turned their attention to the armed wings of the city’s political parties, of which Muttahida is by far the largest.
But few are writing off Mr. Hussain, a wily political player with a long record of survival, just yet.
For much of the 1990s, Mr. Hussain’s supporters waged a street war against the security forces in Karachi, only to ultimately re-emerge stronger than ever.
Since then, he has enjoyed unquestioned support from the city’s Mohajir population — mostly Urdu-speaking families that migrated from India in 1947 — by playing on their sense of grievance at the hands of local ethnic groups, creating a magnetic cult of personality in the process.
This time, however, the challenges also come from within. Mr. Hussain’s stewardship of the party has become increasingly erratic recently, several officials said.
The opposition leader Imran Khan during an anti-government demonstration in Islamabad, Pakistan, last year. Credit Aamir Qureshi/Agence France-Presse — Getty Images
In addresses to party rallies in Karachi, delivered over the phone from London (his usual mode of communication with the party faithful), he frequently appears to be under the influence of alcohol, they said.
During one lengthy tirade on March 30, Mr. Hussain publicly resigned his leadership and urged his followers to take up charity work, only to reappoint himself hours later.
“We never know if it’s going to be happy hour or sad hour,” said one senior official who privately advocated a change in leadership and spoke on the condition of anonymity.
To many, it seems clear that the Pakistani military, which has a long history of meddling in politics, is trying to engineer a change in leadership. Journalists say the videotaped accusations from Mr. Mirza, the death-row convict, bore the hallmarks of a military intelligence operation.
In political circles, the army has started to take informal soundings about a possible successor to Mr. Hussain, the same party official said.
“They want to keep the M.Q.M., but without Altaf or anyone directly associated with violence,” he said.
But experts warn that such a strategy is fraught with danger. “If the M.Q.M. implodes, what will happen to Karachi?” said Laurent Gayer, author of “Ordered Disorder and the Struggle for the City,” a recent book on Karachi. “It seems that few people are thinking about the consequences of a militarized, fragmented party.”
In any event, Mr. Gayer said, Mr. Hussain is unlikely to be unseated through conventional politics, and therefore much hinges on the outcome of the long-running police investigation in London.
Mr. Hussain looked unsteady as he pushed through reporters at the entrance to the London police station on Tuesday. He has said a large sum of money found at his house — about $650,000, party officials say — came from legitimate political donations.
But his circle faces potentially greater peril from a related police investigation into the murder of Imran Farooq, a former ally who was stabbed to death outside his London home in 2010. On Monday, the Pakistan Interior Ministry announced that a suspect in the case had been arrested.
Still, the British police seem mainly interested in two other suspects, both Muttahida supporters, who fled to Pakistan from London just after the killing in 2010.
The police have not brought charges in either case. But just the possibility of a prosecution has visibly destabilized Mr. Hussain’s party and has weakened his grip on Karachi.
For now, though, the most immediate threat is political. The opposition leader Mr. Khan, whose party is close to the military, and Muttahida are running in an important by-election in Karachi on April 23. Mr. Khan has declared his intention to “liberate” Karachi from Mr. Hussain.
“It is time for M.Q.M. and Altaf Hussain to decide whether they want to be a democratic party or want to do politics through a militant wing,” Mr. Khan told reporters last week.
Few believe the choice is that simple. But even among Muttahida officials, there is a gnawing worry about what will happen if Mr. Hussain, who long commanded the respect of figures like Mr. Mirza, suddenly loses control.
“The militants are confused and worried,” another senior party official said. “They don’t want to follow instructions from a man who says one thing in the morning, and another in the afternoon. That’s a worry for us all.”