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The locals called it a peaceful day: five men assassinated in different parts of the city by rival religious or political groups in a country where the color of a man’s religious headdress defines him as foe or friend.

Anees Ahmed, 28, wore the wrong color. He was gunned down near a bus stop by a hit man on a motor scooter, a common method of assassination.

Ahmed was a prominent figure of Unit 74, a branch office of the Mohajir Qaumi Movement, a Sunni militant group that lives a fortress-like existence at Landhi Koramgi Malir in west Karachi.

The Mohajir Qaumi were once allies with the Mutahidda Quaumi before the two split over ideological differences and started a deadly feud. Now, the Mohajir are a militia, allegedly backed by Pakistan’s armed forces. The Mutahidda, an armed group sustained by Muslims who fled India after partition in 1947, have members in the national and provincial assemblies.

The feud is a major source of violence in this tinderbox city of 12 million, where as many as 240 people have been killed in a day. Karachi is a microcosm of the hair-trigger tensions generated by Shiite and Sunni extremists that threaten to inflame the Muslim world, a vast land that stretches from North Africa to Southeast Asia, home to 1.1 billion people, about one-fifth the world’s population.

On a regional scale, the Muslim schism has taken the fundamentalist Sunni regime of the Pakistan-backed Taliban militia in Afghanistan to the precipice of armed conflict with the Shiite Islamic Republic of Iran.

The threat of war in Southwest Asia worries Washington and other capitals because it could spill over into the Middle East and threaten the West’s oil supplies.

Reflecting that concern, U.S. officials announced Thursday that Iranian Foreign Minister Kamal Kharrazi will join an eight-nation meeting next week in New York that also will be attended by Secretary of State Madeleine Albright. It would be the highest-level contact in years between the two nations.

Major oil producers, including Saudi Arabia and the United Arab Emirates, have big stakes in the region. Both nations, with Sunni majorities, have recognized and financed the Taliban regime in Afghanistan. Pakistan has trained and supported the Taliban.

The violence has put on hold plans for energy projects in Central Asia. Unocal Corp.’s multibillion-dollar natural gas pipeline from Turkmenistan through northern Afghanistan to Pakistan was suspended this month.

In Pakistan, the Afghanistan-Iran standoff has intensified sectarian disputes that had festered for years, conflicts often rooted in differing interpretations of the Koran and the prophet Muhammad’s religious teachings.

“The tension in Afghanistan has already spilled over into our streets,” said Asfand Yarawali, the parliamentary leader of the opposition National Peoples Party. “We’ve been saying for 20 years Pakistan should get out of Afghanistan–we had no right to be in there in the first place. Now look what’s happening.”

This week, frenzied mobs fought police and shouted, “Death to the Shiites” in Karachi. They had been incited by the assassination–allegedly by militant Shiites–of Alama Shoab Nadeem, deputy secretary general of the militant Sipa-e-Sahaba Sunni movement, and three of his bodyguards.

The assassination followed Iran’s charges that the Taliban massacred nine Iranian diplomats, including a journalist with diplomatic credentials, and scores of other Shiites when Taliban fighters overran northern Mazar-e-Sharif last month and the town of Bamiyan on Sunday. They were the last Shiite strongholds in Afghanistan.

Shiite extremists, enraged by the slayings in Afghanistan, allegedly gunned down Nadeem and his bodyguards in reprisal. This brought out Sunni militants. By midweek, Sunni mobs in Quetta burned Iranian flags and portraits of the Iranian president. Two mosques near Islamabad were torched. At Lahore, police fought a pitched battle with a mob and detained 200 demonstrators as they gathered near a mosque. The city remained tense.

Bearded and turbaned Sunni militants burned tires on Karachi roads and pelted passing cars with stones Wednesday. The militants have called for a general strike in protest against Iran and the minority Shiites in Pakistan.

“Before any war starts at the Afghan border, they will be at each others’ throats in Pakistan,” warned Sen. Aitzaz Ahsan, a lawyer who argues that Pakistan’s proposed introduction of Islamic law would only expand the sectarian violence.

In Karachi, the rivalry has become a ghetto war. The “troops” live in guarded compounds or residential districts, often surrounded by high concrete walls. The concrete residential blocks with small windows and iron gates near Al Kharam Square are pockmarked with bullet holes.

This is Mutahidda territory, sometimes targeted by Mohajir gunmen who speed by, emptying their automatic weapons.

Altaf Hussain runs the Mutahidda movement from exile in London. His face, painted on gigantic posters and hidden behind sunglasses, frowns down on his followers from the rooftops of the battle-scarred buildings.

Hussain’s party headquarters are behind steel doors and a labyrinth of guard posts. His party has 28 out of 100 representatives in the provincial Sindh assembly and 14 in the National Assembly.

The rival sides have their own mosques inside these compounds, but only the brave dare enter the compound of the Mohajir without powerful recommendations.

The day Ahmed became a martyr, Mohammad Yasin, 22, also was riddled with bullets. It was a killing intended to enrage the faithful who worship at the mosque of Faizani-e-Raza Masjid, where the young man was the muezzin.

(In the old days, a muezzin climbed stairs to the top of the minaret to call the faithful to prayer. Today, he pushes a button to activate a loud speaker.)

“It is easy to make trouble in Karachi. All you need is a gun and someone to shoot. Someone will always wish to revenge the dead person. . . . It never ends,” said a fruit vendor at Tariq Road market.

On the surface, the city shows a placid face: a vast concrete sprawl, drowsy, sluggish, crowded but colorful. Camel-drawn carts plod alongside trucks and mini-buses, their chassis garishly painted in a rainbow of colors and motifs.

Aside from the sectarian clashes, sometimes the violence has other overtones: Law-enforcement officials say the bloody rivalries also involve turf fights over protection, smuggling and extortion rackets.

Karachi is a city of bazaars. Cows wander through a milelong fruit and vegetable market. The ancient goat market still functions down the center of a ring road under construction. Shopkeepers on Tariq Road boast that you can find anything from the West or the East in their shops. Most goods come in as contraband through the notorious Karachi port.

The veil for women isn’t yet common here. Chaperones are.

“People have learned not to register complaints. The police take no sides and all the organizations have powerful patrons. We live in a city under siege by religious extremists and gangs of criminals,” said Anwar Mohammad, a young computer expert.

Wearing their bagris–green, brown or black–young toughs proclaim their loyalties, unconcerned that it makes them potential targets. A martyr’s death is God’s will.

On city roads, a huge finger points at motorists from towering placards, a reminder that Pakistan is girding for what may yet come. “The Army needs YOU,” the posters read.