ISLAMABAD, Pakistan -- The assassination of a prominent lawmaker in Karachi, Pakistan, triggered a wave of revenge attacks that had claimed at least 45 lives as of Tuesday and raised fears of a new cycle of reprisal killings in Pakistan's largest city.

So-called targeted killings, often motivated by political feuds and sectarian divisions, have plagued Karachi for years. But this year, their number has risen sharply, with an estimated 170 people slain in targeted killings and reprisal attacks. Last year, the total was 152, according to government figures.

As in years past, many attacks this year have centered on the rivalry between two powerful political parties, the Muttahida Qaumi Movement and the Awami National Party. The MQM party, which dominates government in Karachi, represents descendants of Indian migrants who settled in Pakistan when the country became independent in 1947. The Awami party, a secular movement, represents Karachi's large Pashtun minority.

The violence that swept through Karachi was fueled by the killing of Raza Haider, a senior MQM leader and a member of the Sindh provincial legislature. Mr. Haider, 51, was attending a funeral Monday at a mosque in Karachi's Nazimabad neighborhood when gunmen on motorcycles appeared and shot him and his bodyguard dead.

Mr. Haider's slaying spurred a wave of as many as 45 reprisal killings by Tuesday afternoon. Dozens of stores, buses and cars were set ablaze late Monday night, as police struggled to stem the violence. At least 93 people were injured.

Dozens of owners closed their shops Tuesday, and traffic on many city streets was almost nonexistent, as residents feared another wave of unrest. Pakistani paramilitary forces were deployed throughout the city to maintain calm. The government also shut down Karachi's colleges.

Fueling the cycle of targeted killings that plagues Karachi every year is the nexus between Karachi's organized-crime leaders and the city's political heavyweights. The affiliations revolve around rival gangs' never-ending battle for the city's prime real estate, which can generate millions of dollars in profits.

MQM leaders stopped short of blaming Mr. Haider's murder on the Awami party, but they accused the ANP of aligning with Karachi's powerful gangs and stoking the city's endless cycle of violence.

"ANP publicly supports the land mafia," said MQM leader Raza Haroon. "We are not saying that ANP is directly involved in the killing of Raza Haider, but they should be investigated."

Amin Khattak, the ANP's provincial general secretary, said MQM's claims about ANP were unfounded.

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