Security forces in Yemen have opened fire at a large protest outside the university in the capital, Sanaa.

也门保安部队向在萨那大学外围进行抗议的人群开火射击。

Anti-Saleh protesters have often faced fierce resistance from security forces
They were trying to stop thousands of people joining a protest camp at the university calling for President Ali Abdullah Saleh to resign.

At least 50 people were injured. Medical sources told the BBC that five were in a serious condition.

There were also reports of protests in other Yemeni cities, amid widespread unrest in the region.

The Yemeni protesters, mostly students, have been camped out in front of the university since mid-February.

They want Mr Saleh to stand down and are calling for more job opportunities, an end to corruption¹, and a fairer distribution of wealth.

As large crowds tried to build up the camp, security forces fired rubber bullets, tear gas and live rounds.

Medics told BBC Arabic that 20 people had been shocked by electric stun² guns（眩晕枪） and that 85 people had suffered the effects of tear gas.

Several thousand women had also joined the march to mark International Women's Day.

Opposition³ spokesman Muhammad Qahtan said the incident had been "a massacre⁴（大屠杀，惨败） ".

It is a crime by security troops against students engaged in a peaceful sit-in," the Associated Press quoted him as saying.

'No teaching'

Tuesday also saw protests in the southern city of Aden and in Ataq.

In Ataq, hundreds of children took mark in anti-Saleh demonstrations⁵ chanting "No studying, no teaching until the president falls," Reuters reports.

In Ibb province, thousands of people took to the streets to demand action against Saleh loyalists who attacked a protest camp on Sunday.

More than 50 were injured in that attack and 18-year-old Omar Atta was killed.

His father told the protest: "My son sacrificed himself, this is my family's gift to the revolution in Yemen."

At least one person was reported to have been killed during a riot at a prison in the capital.

A prison official told AP that inmates⁶ had set blankets and mattresses⁷（床垫） on fire and occupied the central courtyard late on Monday night.

He said guards had fired tear gas and shot into the air but had not managed to subdue⁸（征服，抑制） the violence, which continued throughout Tuesday.

Yemen is one of a number of countries in the North African and Middle East region that have seen increasing unrest since the presidents of Egypt and Tunisia were ousted⁹ in popular revolts（反抗，叛乱） .

Thousands of people have turned out for regular demonstrations in cities including Sanaa, Aden, Taiz and elsewhere, calling for corruption and unemployment to be tackled and demanding the president steps down.

The protests have often been met by riot police or supporters of President Saleh armed with knives and batons¹⁰（警棍） .

The president has been power for 32 years, facing a separatist movement in the south, a branch of al-Qaeda, and a periodic conflict with Shia tribes in the north.

He has said he will not seek another term in office in 2013 but has vowed¹¹ to defend his regime "with every drop of blood".