In Yemen, two key tribes have abandoned their support to President Ali Abdullah Saleh with pressure intensifying on him to resign. Reports from Capital Sanaa says powerful tribal leaders, including those of the Hashid and Baqil have pledged to join protests against Saleh at a gathering north of the capital.The Hashids are considered Yemen's most powerful tribal confederation and include nine clans. Among them the Sanhan tribe had been a bulwark of Saleh's regime for long. The Baqil is the second largest tribe. The two tribes announced they will support the popular uprising against Saleh. The news came as an official denied reports that police killed four people on Friday in an assault on an anti-government protest in Aden. The police blamed a southern secessionist group for the attack. According to an AFP at least 19 people have now been killed in almost daily clashes at anti-regime protests since they erupted 10 days ago.