Security forces on high alert this week under growing threat of violence and bombings following Bhutto killing.
Pakistani security forces, still reeling from the brazen assassination of opposition leader Benazir Bhutto, are on high alert this week for an older but potentially far bloodier threat.
Troops and police have been deployed to areas of high militancy and sectarian tension ahead of the Muslim holy month of Moharram, when minority Shi'ites especially mourn the death of the Prophet Mohammed's grandson seven centuries ago.
Pakistan's recent history of sectarian violence, the dramatic rise last year of suicide bombings and the December 27 murder of Bhutto has some security analysts predicting a bloodbath.
"Given the prevailing security situation in the country we have directed law enforcement agencies to be on high alert to foil any nefarious designs of extremist elements," interior ministry spokesman Javed Cheema told AFP.
"There is a threat perception and we are not going to take any chances. Our security apparatus will be on the highest alert."
Moharram is likely to start Thursday, but the crucial period will come around the 10th day, when hundreds of thousands of Shi'ites take to the streets around the country in a mass display of mourning.
Many weep and thrash themselves bloody as they march in tightly packed crowds, oblivious to the danger from Sunni gunmen and suicide bombers who have targeted them in the past.
The two communities generally live in harmony. But violence linked to extremist groups from both sects has killed more than 4,000 people over the last decade, with some of the bloodiest attacks taking place during Moharram.
"We need special security this time in the wake of recent unrest in the country," said shopkeeper Bismillah Khan, 34, in the southwestern city of Quetta where a suicide bomber killed some 50 people in an attack on a Shiite procession during Moharram in 2004.
"We appeal to both the sects to maintain religious harmony."
Shi'ite areas in the North West Frontier Province face a "two-fold threat," Cheema said, from ordinary sectarian extremists as well as Taliban-style Islamist militants.
Sunni and Shi'ite tribes dug into hilltop villages outside the town of Parachinar, some 150 kilometres west of here on the Afghan border, used heavy weapons including rockets and mortars in clashes only last month.
The latest clashes started on December 22, four days after the Shi'ite Turi and Sunni Mengal tribes signed a ceasefire agreement following weeks of fighting which left more than 100 people dead.
The unrest forced the government to deploy troops and impose a curfew. More troops have been deployed to high ground around the nearby flashpoint town of Hangu, where 22 died in a suicide attack on a Moharram procession last year.
In Karachi, Shi'ite leader Mirza Yusuf Hussain acknowledged that Bhutto's assassination had raised tensions across the country.
Her murder in a gun and suicide bomb attack has been blamed on a local militant linked to Al-Qaeda, but he has denied any involvement.
"This year we realise that the threat is more prominent after the assassination of former prime minister Benazir Bhutto," Hussain said.
"That's why we have agreed with the government to assist the law enforcement agencies with more commitment to compromise on some of our traditions that we have followed in the past."
He said police would receive help checking vehicles and setting up camps for participants.
Captain Mohammad Fazal, spokesman for the paramilitary Rangers in Karachi, a city of 12 million people, said 10,000 troops would be deployed at "all important locations."
"If needed, we have a 4,000-strong force in reserve to be called," he said.
Many of the bloodiest attacks on Shi'ites have been blamed on Sipah-i-Sahaba Pakistan and its shadowy faction Laskar-e-Jhangvi, banned Sunni extremist groups which see members of the minority sect as infidels.
Abdul Ghafoor Hyderi, a Sipah-i-Sahaba spokesman, said the simple solution was to ban all Shi'ite processions.
"We have suggested to the government that to maintain security and save precious lives it is necessary to observe all such religious rituals inside the premises and worship places," he said.