Supporters of the Pakistani opposition party smash a car after setting a vehicle on fire during a gun battle between two rival groups Saturday in Karachi, Pakistan. Pakistan's political crisis descended into violence.

Karachi, Pakistan ? A political crisis threatening President Gen. Pervez Musharraf exploded into violence Saturday when clashes between pro-government gunmen and opposition supporters killed at least 28 people and thwarted a major rally against military rule.

The violence in Pakistan’s largest city, Karachi, was the worst in a two-month crisis shaking the government under Musharraf, a vital U.S. ally who provoked the turmoil by ousting the head of the Supreme Court on March 9.

Gunmen with assault rifles traded fire among bungalows and concrete apartment blocks in the city of 15 million, a major port and home to Pakistan’s stock market. Shipping containers and immobilized trucks blocked streets and men brandished rifles and handguns against a backdrop of burning cars and buses.

The attacks trapped ousted Chief Justice Iftikhar Mohammed Chaudhry at the Karachi airport, unable to attend what organizers hoped to be the largest rally yet calling for Chaudhry’s reinstatement and for Musharraf to step down.

Musharraf loyalists insist that the president remains popular despite resentment of his alliance with the Bush administration to pursue al-Qaida.

But simmering resentment has been unleashed by Musharraf’s removal of Chaudhry, who had a reputation for challenging government misdeeds. Critics accuse Musharraf of removing Chaudhry to protect the president’s plan to seek a new five-year term. The government maintains Chaudhry was ousted because he had abused his office.

Opposition members accused the pro-government Mutahida Qami Movement of launching the attacks, saying that as they attempted to greet Chaudhry at the airport, they were attacked by MQM members with batons and guns. The MQM is a coalition partner in both Sindh province, of which Karachi is the capital, and in the federal government.