Six university students were wounded in clashes between rival groups at Sanaa University on the first day of school Saturday, after fighting in the capital overnight between competing army units left one dissident soldier dead.
Meanwhile, renewed clashed between the army and fighters linked to Al-Qaeda in the southern city of Zinjibar left six soldiers wounded.
Students who backed a resumption of classes and those who did not came to blows and threw stones and other projectiles at each other, according to those involved and a medical official.
Shouting "No lessons, no teaching, before the ouster of the president (Ali Abdullah Saleh)," hundreds of students marched through the university campus. calling for a boycott of classes and trying to keep their classmates from going to their lessons, an AFP journalist said.
A professor, Hassan Kahlani, told AFP he had temporarily stopped his students from leaving their lecture hall at the end of their class.
Only around 15 percent of students attended classes on the first day of the academic year, according to students.
Access to the university was controlled by military forces loyal to dissident General Ali Mohsen al-Ahmar, whose troops control Change Square, next to the university where protesters have been calling Saleh's ouster since January.
Tanks and armoured vehicles were stationed at the entrance to the campus and armed civilians were seen along the walls of the university, and the arts and languages departments remained closed, students said.
Minister of Higher Education Saleh Ba-Surah said he had met with General Ahmar on Saturday, and had asked him "not to involve students in the political crisis".
Overnight, fighting in the capital between rival army units left one dissident soldier dead, witnesses and medics said.
"Clashes broke out between soldiers from the Fourth Brigade (loyal to the regime) and the youths' security committee backed by dissident troops from the First Armoured Brigade" headed by Ahmar, witnesses said.
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The fighting, in which machine guns were used, took place at the eastern entrance to Change Square, where anti-Saleh protesters have camped since February, witnesses told AFP.
"One soldier was killed and five members of the youths' security committee were wounded," said medics.
Saleh's troops fired on the square when protesters, whose numbers have been rising, tried to expand their sit-in, witnesses said.
The protesters' security committee, backed by Ahmar's troops who have protected the square since March, responded, they added.
Tensions have been rising in Sanaa, with government forces fortifying their positions and Ahmar soldiers deployed in areas of the city they control.
Separately, the Saleh's troops fired six mortar rounds overnight at the home of prominent opposition tribal chief Sheikh Sadiq al-Ahmar in Sanaa's northern Al-Hasaba district, without causing casualties, his office said.
In the southern city of Zinjibar, six soldiers were killed in renewed fighting with fighters linked to Al-Qaeda, a military official said.
"The army is facing resistance from al-Qaeda fighters in eastern Zinjibar," the town in Abyan province that authorities said was recaptured last week from militants, the official said.
"Fresh fighting broke out Saturday at dawn and lasted three hours. Six soldiers were wounded," the official added. He said there were "dead and wounded" among the militants, but gave no numbers.
The government announced on September 10 that troops had liberated Zinjibar from the Partisans of Sharia (Islamic Law) militants who overran it in May.
The incidents come as Yemen teeters on the verge of collapse following months of anti-government protests and growing influence of Al-Qaeda in the Arabian Peninsula (AQAP), as the embattled Saleh remains absent from the scene.
Saleh is receiving medical treatment in Saudi Arabia following a June bomb blast on his presidential compound. He has resisted regional and international calls for him to step down despite more than eight months of nation-wide protests.
Last week, US intelligence chiefs said Al-Qaeda's core leadership has been severely damaged but the network's affiliate in Yemen has exploited unrest there and poses a growing danger.