Yemeni President Ali Abdullah Saleh, in power since 1978, said Monday only defeat at the ballot box will make him quit, even as MPs joined thousands of protesters in Sanaa calling for his departure. In the country's south, police shot dead a protester in the regional capital, Aden, where protests have raged killing 12 people and wounding dozens since February 16, medics and witnesses said. "If they want me to quit, I will only leave through the ballot box," Saleh told a news conference as the protesters, including opposition MPs, gathered outside Sanaa University. "The opposition are raising the level of their demands, some of which are illicit," the Yemeni leader said. Saleh, whose long reign makes him one of the Middle East's great survivors, said the protests were "not new," accusing his opponents of having been behind the demonstrations for a while. Opposition MPs, who vowed to take to the streets in a statement issued on Sunday, joined students who have been protesting for the past nine days. Security forces surrounded the protesters as they gathered in a nearby square carrying banners declaring: "People want change," "People want to overthrow the regime" and "Leave". The Common Forum, an alliance of parliamentary opposition groups has urged all of its parties on Sunday to "join the protesting youths... in their demonstrations against oppression, tyranny and corruption," in a statement received by AFP. Responding to Saleh's calls earlier this month to resume dialogue, stalled since October, the parliamentary opposition had refrained from calling for protests since February 3. But "after bloodshed and the fall of victims, and after the government has sent its thugs onto the streets... we insist that there is no dialogue with bullets and batons" and with a regime "that brings thugs to occupy public places and terrorise people," the statement said. Protests, have become increasingly violent in poverty stricken Yemen despite calls by Saleh -- who was elected to a seven-year-term in September 2006 -- urging dialogue to form a government of national unity. Farther south, in Aden, Yemeni police shot dead a protester and wounded four others on Monday, witnesses and medics told AFP. Ali al-Khalaqi died of his wounds at a hospital in Aden. One of the four others receiving treatment is seriously wounded, medics told AFP. Khalaqi is the 12th protester to die in the port city since February 16, according to an AFP tally. Dozens of people have been wounded, including seven soldiers. Meanwhile, Yemeni clerics issued a statement on Monday prohibiting the use of force against protesters, which they described as a "crime," and calling for a ban on arbitrary arrest and torture. "Any act of beating or killing of protesters is a deliberate crime," said the association of Yemeni clerics headed by Sheikh Abdul Majid Zindani. The clerics demanded a ban on "arbitrary arrest and (all forms of) torture" and said that pro-government rallies should be held away from protest demonstrations to avoid the deadly clashes of recent days. Zindani is blacklisted as a "global terrorist" by Washington for his suspected links to Al-Qaeda but the association groups clerics of both Yemen's Sunni majority and its Zaidi minority, from which under-fire Saleh hails. Clashes between pro- and anti- Saleh demonstrators left dozens wounded last week. Saleh has outlived the Cold War division, civil war and an Al-Qaeda insurgency but is now scrambling to see his term through to the end as sustained popular uprisings in Sanaa and Aden test his grip on power. The veteran strongman had already pledged not to seek re-election after the expiry in 2013 of his current seven-year term as head of the impoverished country, and has made other concessions aimed at stemming popular discontent.