Thousands of angry Pakistanis protested Sunday against a U.S. airstrike that killed civilians, chanting "Long live Usama bin Laden!" as anti-American rallies in the country entered their second week.

Pakistani authorities, meanwhile, arrested a relative of a man suspected of hiding the bodies of four suspected Al Qaeda operatives believed killed in the Jan. 13 attack, a security official said on condition of anonymity because he was not authorized to speak to the media.

The man, who was not identified, was arrested in Damadola, the remote hamlet near the Afghan border where U.S. missiles struck Jan. 13, the official said. The suspect was related to Faqir Mohammed, a pro-Taliban cleric who intelligence officials believe was responsible for hiding the bodies.

"We are investigating his links" to the extremists targeted in the airstrike, the official said, adding that authorities also were seeking Mohammed and another cleric believed to have helped hide the bodies.

Pakistani officials say 13 other civilians also were killed in the attack, including women and children. The attack reportedly targeted Al Qaeda's No. 2 leader Ayman al-Zawahri, who was not there.

About 5,000 demonstrators assembled on a dry riverbed in a mountain market town near the site of strike, shouting "Long live Usama bin Laden!" and "Death to America!" They also burned effigies of President Bush.

"America is the biggest terrorist in the world," said Maulana Mohammed Sadiq, a lawmaker in the Jamiat Ulema-e-Islam party that helped organize the protest. "America bombed innocent people inside their homes."

The rally was the latest in a string of protests in Pakistan's biggest cities over the missile strike. The assault has sparked friction between Islamabad and Washington and widespread outrage in the Islamic nation of 150 million.

Pakistan authorities have said they are looking for militants who might have survived, but security forces have not visibly stepped up maneuvers in border regions where anger runs high among the 3.2 million residents.

The military still mans ubiquitous checkpoints in the area, but analysts say Pakistan is taking a low-profile approach so as not to enrage local people with large-scale offensives that may cause more civilian casualties.

The military has about 70,000 soldiers in the area, although an Associated Press reporter who has visited Damadola three times since the attack has not seen a single uniformed soldier in town.

Hundreds of Al Qaeda and Taliban militants, including bin Laden and al-Zawahri, are believed to be hiding in the rugged mountains along the porous Pakistan- Afghanistan border.

Army spokesman Brigadier Shahjehan Ali Khan could not estimate how many militants were hiding there, but officials in the past have said they include hundreds of Arab, Central Asian and Afghan fighters.

On Saturday, Pakistan's President Gen. Pervez Musharraf told visiting U.S. Undersecretary of State Nicholas Burns that the United States cannot repeat such attacks, a Foreign Ministry official said. Foreign Minister Khursheed Kasuri called the assault "counterproductive" given the "prevailing public sentiment."

They were Musharraf's first publicized comments on the attack, as the leader tried to soothe mounting disapproval of his backing of the U.S.-led war on terror.

The attack was believed to have been launched by a predator drone based in Afghanistan, where the U.S. has about 20,000 troops. Pakistan does not allow U.S. forces to pursue militants across the border or launch strikes without permission.

Shahid Shamsi, a spokesman for the opposition Mutahida Majlis-e-Amal, or United Action Forum, said Musharraf's comments came "too late."

"He made the statement under the pressure that has been building up in the country," Shamsi said.

Pakistan officials those killed in the strike may have included Egyptian master bomb maker Midhat Mursi, who has a $5 million bounty on his head from the U.S. government.

Pakistan authorities suspect Al Qaeda operatives gathered at a dinner last week in Damadola to plan attacks for early this year in Afghanistan and Pakistan.