Updated

Yemen's embattled president on Sunday sought a way out of the political crisis gripping his impoverished Arab nation, offering to oversee a dialogue between the ruling party and the opposition to defuse the standoff with protesters demanding his ouster.

The offer by the U.S.-backed Ali Abdullah Saleh — which opposition groups swiftly rejected — came as protests calling for his ouster continued in at least four cities around the country for the 11th straight day.

A 17-year-old demonstrator was killed Sunday evening in the port city of Aden when the army opened fire to disperse a march there, bringing the death toll to nine since the protests began.

Much is at stake in Yemen — a deeply troubled nation strategically located at the mouth of the Red Sea and next door to the world's largest oil reserves. Saleh's weak government is already under pressure from a southern separatist movement and disaffected tribesmen around the country.

The U.S., however, is most worried about an al-Qaida offshoot that has taken root in Yemen's mountains to plot attacks beyond the country's borders, including the failed attempt to blow up a U.S.-bound airliner in December 2009.

Saleh — in power for three decades — is quietly cooperating with the U.S. in efforts to battle the al-Qaida franchise, but his government exercises limited control in the tribal areas beyond the capital. The U.S. gives Yemen military aid and training.

Saleh's rule continues to show signs of resilience in the face of the sustained protests that have seen security forces and regime supporters battling demonstrators, mostly university students.

Yemen is a tribal society where almost every adult male has a firearm. A decision by the country's major tribes to take sides in the standoff between Saleh and his critics could decide the president's fate.

Protests continued Sunday, with 3,000 university students marching in Sanaa, the Yemeni capital. Demonstrations were also held in a number of districts near Aden, the town of Taiz and the province of al-Hadida.

The protests pose the most serious challenge to Saleh's rule to date.

He has already made a series of concessions, pledging that his son would not succeed him and that he would not seek another term in office. On Sunday, he repeated his offer for negotiations.

"Dialogue is the best means, not sabotage or cutting off roads," Saleh told a news conference. "I am ready to sit on the negotiating table and meet their demands if they are legitimate," said the Yemeni leader, who warned against "infiltrators" seeking to divide Yemenis and sabotage their country.

A group of opposition parties refused to engage in dialogue while security forces continued to suppress demonstrations.

"No dialogue with bullets, clubs and thuggery," the group said in a statement Sunday.

The protesters have been inspired by uprisings in Egypt and Tunisia.

Marching students on Sunday burned the flag of Saleh's party and tore up photos of the president. Some wrote "Get out! Get out!" on the sidewalk, while others carried signs reading "Get out Ali for the sake of future generations."

Riot police surrounded them to keep them in a square in front of the university but did not intervene. On Sunday evening, more than 1,000 protesters remained in the square, saying they'd remain until the regime fell.

In the southern city of Aden, demonstrators led a number of small protests. A health official said one 17-year-old marcher was killed when the army fired to disperse about 100 protesters, bringing the city's death toll to five in recent days.

Security officials and activists both said about 80 people had been arrested in the city.

Officials spoke on condition of anonymity because they were not authorized to speak to the media.