KARACHI, 10 May — Authorities detained hundreds of militants yesterday as Pakistani, US and French investigators searched for any links between the Al-Qaeda network and a car bomb attack on Wednesday that killed 11 French engineers and three Pakistanis.

Twelve Frenchmen wounded in the suicide bombing returned home aboard a flying military hospital. The wounded French nationals were ferried from hospital by a fleet of ambulances with a team of doctors to Karachi Airport, where a German Airbus A310 aircraft took them to Paris.

French Prime Minister Jean-Pierre Raffarin met them at Orly airport in Paris, together with families of the wounded. He said the bombing had targeted “nations engaged in the fight against terrorism in Afghanistan.” “We are obviously struck by the extremely organized conditions in which this attack occurred,” Raffarin told reporters at the airport.

After visiting the site of the blast and the injured French citizens, French Defense Minister Michel Alliot-Marie said the bombing was “part of the larger terrorist movement against which the international coalition is fighting.”

She praised Pakistan’s President Pervez Musharraf for his “brave choice” to join the US-led war on terrorism after Sept. 11, and said the attack only strengthened France’s determination. “We have to fight terrorism till it’s eliminated,” she said.

Many militants in Pakistan have close links to Al-Qaeda. They have vowed revenge for Musharraf’s banning of five militant groups after he abandoned Afghanistan’s Taleban regime and sided with the United States.

Musharraf has called the bombing an attempt to “destabilize” Pakistan and “weaken its resolve” in the fight against “international terrorism.”

Information Minister Nisar Memon, who met with Alliot-Marie, insisted Pakistan would not be deterred and had already taken “more measures to combat terrorism.” He did not elaborate.

But a top Interior Ministry official, Tasneem Noorani, said “a number” of activists belonging to the outlawed radical groups have been arrested across the country. “We are expecting more arrests as the raids are still in progress,” he said, declining to elaborate.

However, Interior Ministry officials, speaking on condition of anonymity, said at least 298 suspected members of Jaish-e-Muhammad, Sipah-e-Sahaba, Lashkar-e-Taiba and other groups were arrested in the crackdown, which was expected to last several days.

After Musharraf banned the groups in January, more than 2,000 militants were arrested but later released. Officials said those militants who had been cleared were not being arrested in the current sweep.

In Karachi, three FBI agents spent 90 minutes sifting through the twisted, charred skeleton of a Pakistan Navy shuttle bus blown apart by what Pakistani police believe was a suicide bomber in a nearby car. Alliot-Marie, who arrived to consult with Pakistani officials in the wake of the attack, said French investigators were already in Pakistan as well.

With security forces on maximum alert, paramilitary rangers set up posts and concrete barriers at major hotels and key places frequented by Westerners. The roads in front of the US Consulate and the British Deputy High Commission in Karachi were closed, creating massive traffic jams in the city of 14 million. Lonnie Kelley, a US Consulate spokesman, said Westerners in Karachi were “extremely nervous.” “So far we are not telling anybody to go home,” he said. “But we have asked them to take extra precautions.” Atta Ansari, a spokesman at the French Consulate, said French firms, including Indo Suez Bank and Air France, were likely to continue their operations. But many Westerners, including Americans and French, left Karachi hours after the attack, and others were planning to leave, major hotels and travel agents said.

“I am going out of here on the first flight,” said one woman, who identified herself only as Lisa, standing nervously beside an armed Pakistani Marine in a hotel lobby. She refused to disclose her nationality or explain the purpose of her visit here. “We have been advised to be very careful. ... I can’t talk to strangers.”

A senior police officer in the populous Punjab province, Chaudhry Masood, said known radicals had been rounded up as a precaution. He warned foreigners working on a thermal power plant in the province to limit their movements.