PESHAWAR, Pakistan — Islamic groups vowed Monday to keep up their anti-American protests over a purported CIA airstrike that Pakistan says killed innocent civilians instead of the apparent target — al-Qaida's No. 2 leader.

For the second straight day, thousands of Pakistanis poured into streets in cities across the country on Sunday chanting "Death to America" and demanding U.S. troops leave Afghanistan.

Protesters believe Friday's attack — in which missiles struck a Pakistani village near the Afghan border — was the work of U.S. forces in the neighboring country. The United States has 20,000 troops in Afghanistan searching for Taliban and al-Qaida, and Pakistan says it has not given the Americans permission to pursue their enemies across the border.

"There will be more ... bigger protests," said Shahid Shamsi, spokesman for an alliance of Islamic groups.

"Pakistani civilians, including children, were killed," he said. "Principles cannot be broken in the name of (fighting) terrorism."

Two Pakistani intelligence officials said Ayman al-Zawahri, Osama bin Laden's top lieutenant, had been invited to a dinner in the village to mark the Islamic holiday of Eid al-Adha but passed it up and sent some aides instead.

Investigators were trying to see if they were among at least 17 people killed the attack, which destroyed three houses in the Pashtun hamlet of Damadola, the officials said. They spoke on condition of anonymity because of the sensitivity of the issue.

Pakistani officials have strongly condemned the strike, without directly blaming the United States. The United States hasn't commented on the incident.

A senior army official told The Associated Press on Sunday that "foreigners" were reported in the area around Damadola, which is four miles from the Afghan border, but he said there was no information al-Zawahri was among them.

Many in this nation of 150 million oppose the government's participation in the U.S.-led war on terrorism. The strike was one of several suspected U.S. attacks along the frontier aimed at militants.

Many al-Qaida and Taliban combatants, including al-Zawahri and bin Laden, are believed to have taken refuge in the rugged mountains along the Afghan-Pakistani border.