Bomb Outside Karachi Mosque Kills 12 : Pakistan: Attack fans hatreds, increases pressure for decisive government action to restore order in country’s largest city.

In a lethal attack that fanned anti-U.S. and sectarian hatreds in Pakistan, a time bomb hidden inside a motorcycle exploded with devastating power outside a Shiite mosque filled with worshipers Friday, killing 12 people, including seven children.

At least 28 other people were injured--half of them were 14 or younger and one was a 3-year-old girl--in the deadliest bombing in violence-plagued Karachi since a car packed with plastic explosives killed more than 100 people in 1984.

The pressure mounted on Prime Minister Benazir Bhutto to take decisive action to restore order to her country’s largest city.

Bhutto flew to Karachi on Friday night and planned to meet top law-and-order officials today.

At the mosque, the mullah was giving the final blessing Friday at the midday prayer service when the bomb exploded. The full force of the blast was taken by people outside, including children waiting at the mosque’s entrance gate for their parents, and vendors and beggars, some of them youngsters.

Shakeel, a 2-year-old boy, was killed. Salma, a 7- or 8-year-old girl who was begging, was struck by metal splinters in the head and leg.

“It was a tremendous explosion,” said worshiper Shabhihul Hassan, 45. “I was standing at the main gate, inside. I ran into the mosque, then noticed I was bleeding myself.”

The jobless man, his long white smock soaked in blood around the left armpit, was hit in the upper chest by shrapnel or flying debris.

In the last 3 1/2 months, more than 500 people have been slain in violence and ethnic, political and sectarian turmoil in Pakistan’s trade and business center. In the opinion of many, the Karachi killings and the fear and disorder they sow threaten the very survival of Bhutto’s government.

But Bhutto, a voice for moderation and an American friend in the Islamic world, had been downplaying the scope of Karachi’s troubles in recent days and trying to reassure U.S. and other Western investors that they can safely place their money and enterprises in Pakistan.

“What I want to emphasize is that it is not as though the trouble is all over Pakistan or all over Karachi,” she told a conference of multinational companies in Singapore on Thursday before returning to Pakistan. “There is trouble in a part of Karachi, which is unfortunate. The irony is that the other part of Karachi is flourishing.”

In November, Bhutto withdrew the army from Karachi’s streets, ending its 29-month-old “Operation Cleanup.” Despite her assurances that police and the paramilitary Rangers could handle things, the wave of terror and crime mounted.

Friday’s bombing gave another push to the painful ordeal of this teeming city on the Arabian Sea, home to more than 10 million people. In Malir and other parts of eastern Karachi, seven people were shot dead as Shiite Muslims and members of Pakistan’s majority Sunni sect began attacking one another, police said.

Police began arresting Sunni activists, apparently seeing them as the likeliest suspects in the bombing. The main leader of Karachi’s Sunnis, lawyer Hafiz Ahmed Bakhsh, was arrested 3 1/2 hours after the explosion and charged with murder.

Bomb disposal officers investigating the attack said the explosive charge had been concealed in the battery compartment of a red Yamaha motorcycle parked near the mosque’s main gate. The cycle was reduced to mangled wreckage by the blast, and a minivan, a car and two other motorcycles were wrecked or burned.

Senior police bomb disposal expert Moinuddin estimated that 4 1/2 pounds of plastic explosive--or a powerful bomb material known as RBX--had been used. The charge and timing device were surrounded with ball bearings or shrapnel to increase the device’s killing power, Moinuddin said.

As is typical in Karachi’s agony of violence, in which more than 1,260 people have been killed since the start of 1994, there was no claim of responsibility.

Allama Baqir Najfi, the local leader of the Shiite Tehrik-i-Jafria religious party, blamed the Sind provincial government, which is allied to Bhutto, and “American and capitalist agents,” and said they were behind earlier attacks on Shiite sanctuaries as well.

On Friday evening, as Sunnis and Shiites exchanged gunfire, Shiite activists set a bus afire in Malir.

Shiite and Sunni extremists have been fighting in earnest in Karachi since last year, and in 1995 alone, at least 18 shootings and massacres inside and outside mosques have occurred. But some police suspect that the apparent sectarian violence may be the work of hired killers and that religion plays little if any part in it.

Meanwhile, the gunmen responsible for Wednesday’s ambush of a van belonging to the U.S. Consulate remained at large. The U.S. government has offered a reward of up to $2 million for information leading to their arrest.

Two Americans, Jackie Van Landingham, 33, a secretary from Camden, S.C., and Gary C. Durell, 45, a communications technician from Alliance, Ohio, were killed in the attack.