Government forces in Sanaa unleashed some of the heaviest shelling yet against their tribal rivals in a dramatic escalation of the conflict.
For months, youth-led protesters have tried to drive out Saleh peacefully. But their campaign has been overtaken and transformed into an armed showdown between Yemen''s two most powerful families, the president's and the al-Ahmar clan.
The al-Ahmar family heads the country's strongest tribal confederation, which has vowed to topple Saleh after 33 years in power.
Their nearly two week-old battle in Sanaa raises a dangerous new potential in Yemen: that tribal fighting could metastasize and spread across the impoverished nation. Tribes hold deep loyalty among Yemen's 25 million people, and the death of a member can easily draw relatives into a spiral of violence.
On Thursday, tribesman attacked security forces in the city of Taiz, south of the capital, apparently to avenge deaths of protesters there last week or to protect them from new crackdowns. Saleh's security forces have cracked down hard on the street protesters, killing well over 100 since February, but until now tribal fighters had stayed out of the fray.
Attack suggests other tribes may see the fighting between Saleh and al-Ahmar as a sign it is time to get out their guns as well.
With a potentially decisive battle for the capital looming, the campaign to oust Saleh is increasingly taken out of the hands of those who launched it: the hundreds of thousands who have been holding daily protests in the capital and other cities. Led by youth activists, they had taken their inspiration from peaceful uprisings that toppled the leaders of Egypt and Tunisia.