The announcement is a blow to President Saleh, in particular because one of the chiefs is from his own tribe, the Hashid.

The leaders said in a statement Saturday they have also quit the president's ruling political party.

Earlier Saturday, medical officials said four people died after being injured in clashes Friday between anti-government protesters and security forces.

Tens of thousands of demonstrators rallied Friday in Yemen's capital, Sana'a.  

Protesters took to the streets after Friday prayers.  They gathered near Sana'a University, the site of a string of anti-government demonstrations during the week.

On Wednesday, at least seven members of parliament submitted their resignations from the ruling party to protest the government's violent response to the demonstrations.  They said they would form an independent bloc in the legislature. 

At least 16 people have died in Yemeni demonstrations since the protests began earlier this month.