SANAA (AFP) - Yemen's embattled President Ali Abdullah Saleh on Friday gave a cool response to a Gulf plan for him to quit, even as massive crowds returned to the streets to demand his immediate ouster. While tens of thousands of anti- and pro-Saleh demonstrators packed two different locations in Sanaa, suspected tribesmen and Al-Qaeda militants killed 22 people, all but two of them soldiers, and captured dozens of others in separate attacks over a 24-hour period, security and tribal sources said on Friday. "Al-Qaeda militants ambushed a military patrol near Safer (oil fields), in (the eastern province of) Marib, killing 11 soldiers," a security official in Sanaa said. The assailants used machine-guns in Friday's attack. Another soldier was shot dead by unknown gunmen in the restive southern province of Abyan. "We stress that we will hold on to the constitutional legitimacy, in loyalty to our people, as we categorically reject the attempted coups on freedom, democracy, and political pluralism," Saleh told regime supporters in Sanaa. In a cool reaction to a Gulf plan for him to step down within 30 days, Saleh said he welcomed the initiative but only "within the framework of the constitution," signalling he could try to serve out his term until 2013. As on past Fridays, a huge rival rally by anti-regime protesters massed a few kilometres (miles) away kept up the pressure for Saleh's immediate departure on what they branded a "Last Chance Friday." An AFP correspondent said the gathering covered a four-kilometre (2.5 miles) stretch, in what appeared to be the largest anti-Saleh rally since protests erupted in late January. Yemeni army and police were deployed in force to prevent clashes between the two camps. In the latest version of the Gulf Cooperation Council (GCC) initiative, the president would submit his resignation to parliament within 30 days, with a presidential vote to be held within two months. Parliamentary opposition groups are still mulling the plan, but the spokesman of the Common Forum coalition said that "forming a national unity government while the president is still in office is not accepted." "The president's departure is essential to any solution," he told AFP. Protesters on the streets on Friday dismissed the proposal out of hand. "Neighbouring countries: no negotiations, no dialogue," read posters carried by demonstrators, referring to the plan under which Saleh would hand over power to his deputy, Vice President Abdrabuh Mansur Hadi. "No initiative no initiative, you should only leave (Saleh)," chanted a group gathered near Hadi's residence. A motor of the revolt, the "Peaceful Revolt Youth," on Friday renewed its rejection of the GCC initiative. The cause was that the proposal does not call for Saleh's immediate departure and grants immunity from prosecution to the president, family and aides, "who are all killers," it said in a statement. The group called for a nationwide general strike on Saturday. Anti-Saleh protesters also rallied across Yemen on Friday, as a Muslim cleric leading weekly prayers in the flashpoint city of Taez also said the GCC initiative was unacceptable. Thousands marched in the main southern city of Aden demanding Saleh's immediate ouster. They chanted: "Ali you villain, our blood isn't cheap" and "Ali go." "We refuse any Gulf or international initiatives," read one banner, witnesses said. Similar protests were also held in Lahij, Hadramut and Shabwa, in the south, witnesses said. Saleh has since January faced anti-regime protests calling for his ouster in which more than 130 people have been killed in clashes with security forces and rival demonstrators. An emailed statement from Yemen's embassy in Washington said on Thursday that GCC chief Abdullatif al-Zayani had presented the latest proposal to Saleh and the opposition, with his ruling party expected to respond within 24 hours. A defiant Saleh, who has ruled Yemen for 32 years, publicly insists on sticking to the constitution in any transfer of power. Amid the political turmoil, armed tribesmen and suspected Al-Qaeda militants killed 20 soldiers, and captured dozens of others in separate attacks over a 24-hour period, security and tribal sources said. Two tribesmen were also killed.