Four Arab men have been arrested in the Iraqi city of Najaf in connection with Friday's bombing at a Muslim shrine that killed at least 107 people and injured more than 140. Iraqi authorities say the men have close ties with Osama bin Laden's al Qaeda terrorist network.

Iraqi police said Saturday the four were non-Iraqi Arabs who were arrested shortly after the explosion. The blast was described as similar to recent attacks at the United Nations headquarters and the Jordanian embassy in Baghdad.

U.S. officials have said that foreign terrorists aiming to destabilize the country have been coming across Iraq's porous borders from Syria, Saudi Arabia and Iran.

Thousands of people thronged the area in Najaf where Friday's bomb exploded outside Iraq's most holy Shia Muslim shrine. Carrying banners and chanting, the crowds denounced the bombing and vowed to avenge the attack that now threatens the delicate balance of religious and political power in the war-torn country.

Angry Shiites initially blamed the bomb on remnants of Saddam Hussein's regime, but they also showed growing anger toward U.S. forces for failing to provide security that could have prevented such an attack.