A heavy gun battle erupted between embattled Yemeni President Ali Abdullah Saleh's security forces and fighters from Yemen's most powerful tribe, which defected to the opposition. The gunbattles rattled the northern Sanaa neighborhood of al-Hasba, sending families fleeing in panic. Dozens of police vehicles blocked traffic on main streets leading to al-Hasba. The clashes occurred near the house of Sheik Sadeq al-Ahmar, leader of Yemen's most powerful tribe, Hashid, to which Saleh himself belongs. Al-Ahmar announced that he has joined the popular uprising that began trying to oust Saleh in March. Monday's clashes came one day after new turmoil swept across the capital as Saleh refused again to sign an agreement calling for him to step down in 30 days.