Suspicion intensified yesterday that a suicide car bomber who killed three US soldiers training Pakistani troops along the Afghan border had inside information on their movements.

If confirmed that Wednesday's suicide attack was aimed at the Americans, it would indicate an increased sophistication in militant tactics, as well as potential infiltration of extremists in Pakistani security forces.

Thousands of Pakistanis in at least four cities, meanwhile, protested a New York jury's conviction of a US-educated Pakistani woman for shooting at American security officials in Afghanistan — shouting anti-US slogans and burning the Stars and Stripes.

The attack on US forces occurred in Lower Dir, a northwest district believed to be a crossroads for al-Qaida and the Taliban. The blast also killed three schoolgirls and a Pakistani paramilitary soldier. Two more US soldiers were among dozens wounded.

Police official Naeem Khan said Thursday that authorities were investigating whether the suicide bomber knew the soldiers would be passing through Shahi Koto town and which vehicle to target in the five-car convoy, which also included Pakistani troops.

Such convoys usually include green military vehicles carrying armed troops who are clearly visible. The Pakistani forces could also have been the target as they have frequently been over the past several years.

"We launched a massive search in the area yesterday, and now about 35 suspects are in our custody, and we are questioning them in an effort to trace those who orchestrated the suicide attack," Khan said. "God willing, we will capture those responsible for this carnage."

Local resident Gohar Khan said he saw a small car attack the convoy.

"As soon as the convoy appeared it rushed to that place and exploded," he told The Associated Press.

The soldiers killed were part of a small group of American troops training members of Pakistan's paramilitary Frontier Corps.

Training local forces is considered an important way to reduce the threat of militants using Pakistani soil as a staging ground for attacks on Western troops in Afghanistan, especially since Pakistan does not allow US combat troops on its territory.

The soldiers' deaths were the first known US military fatalities in nearly three years in Pakistan's Afghan border region.

The latest attack drew rare attention to the training program, which officials rarely discuss because of anti-American feelings here.

That sentiment flared Thursday as demonstrators protested a New York jury's conviction of Aafia Siddiqui, a Pakistani woman accused of shooting at American security personnel who came to interrogate her after her arrest in Afghanistan' s central Ghazni province.

Many Pakistanis believe the US has fabricated the charges. Some suspect the Americans had held the thin neuroscience specialist in a secret prison — allegations the US denies. Siddiqui had been missing for five years before being picked up in Afghanistan in 2008.

A Manhattan federal jury convicted Siddiqui on Wednesday on two counts of attempted murder, though it found the act was not premeditated. Siddiqui was also convicted of armed assault, using and carrying a firearm, and assault of US officers and employees.

Pakistanis denounced the verdict against Siddiqui, a devout Muslim who studied at the Massachusetts Institute of Technology and Brandeis University before returning to Pakistan following the Sept. 11, 2001, attacks.

"We hate America," "We hate US judiciary," and "Down with the US," read some of the signs carried by burqa-clad women protesting in the southern city of Karachi, the hometown of Siddiqui's family.