It has been a tough weekend for Yemen's President Ali Abdullah Saleh. On Saturday, two chiefs from his tribe joined with growing numbers of protesters calling on him to step down.
On Sunday, the mainstream opposition parties promised to hold anti-government rallies early in the week.
"We call on all the citizens to come out Tuesday and condemn the regime for its crimes," the Joint Gathering, an umbrella organization composed of seven opposition parties, announced.
Saleh, who initially invited protesters to talk about the issues and promised not to use force against them, appeared to have changed his position.
He said Saturday his security forces would not hesitate to "defend the security of the nation as well as the unity, freedom and democracy."
"We will fight to the last drop of blood," Saleh said.
Saleh, who has governed Yemen for 32 years, has helped the U.S. In its fight against the al-Qaeda network.
AP contributed to this report.