Security forces in Yemen have opened fire on peaceful protesters in the capital Sanaa on Tuesday, wounding at least 75 people demonstrating for an end to President Ali Abdullah Saleh's 32-year rule.
Three of the wounded were in a serious condition, according to medical sources.
Policemen and security agents in civilian clothes opened fire as they tried to prevent people from joining thousands of
protesters who have camped out for weeks in front of Sanaa University, the epicentre of the demonstrations.
Al Jazeera's Hashem Ahelbarra, reporting from the capital Sanaa, said the security forces were "clearly given orders to disperse the crowd."
"This is a dramatic turn of events that will likely raise tensions. The protesters were trying to move to Taghyeer Square, and the government seems to have panicked," he added.
Our correspondent points out that the shooting comes few weeks after president Saleh pledged to protect peaceful protesters.
There was no immediate government comment.
Police brought out water cannon and placed concrete blocks around Sanaa University, the rallying point for anti-Saleh protest that had been quiet in recent days, after weeks of fierce clashes across the country between government loyalists and protesters that killed at least 27 people.
Separately, around 10,000 protesters marched in the city of Dhamar, 60 km (40 miles) south of Sanaa, residents said by telephone. Dhamar is known for ties to Saleh and is the hometown of Yemen's prime minister, interior minister and head judge.
"Leave! leave!" the protesters shouted in Dhamar, just two days after Saleh loyalists there held a similar-sized rally. Protesters also pelted a municipal official with rocks.
Burgeoning protests fuelled by anger over poverty and corruption, and a series of defections from Saleh's political and tribal allies, have added pressure on him to step aside this year even as he pledges to stay on until his term ends in 2013.
Meanwhile, three prisoners at a Sanaa prison were reported killed and four others injured, Sharif Mobley, an inmate, told Al Jazeera via phone.
Dozens more were injured as a consequence of the unrest, which began on Monday, when around 2,000 prisoners staged riots, taking a dozen guards hostage.
The inmates set their blankets and mattresses on fire before occupying the prison's main courtyard, an official who declined to be named because he is not authorised to speak to the media said.
The guards fired tear gas and gunshots into the air but failed to subdue the prisoners, the official added.
"At the moment there is no violence, there is no fighting," Mobley said on Tuesday morning, "but the situation is really looking very bad".
"The offices of the prison official have been burned down and the guards have all left and are now outside," he said.
"Authorities are outside the prison gates and we are inside the prison. We don't want to make any problems and are afraid for our lives."
Al Jazeera's Hashem Ahelbarra, said the "situation has not yet been contained".
"We have been told by different sources and inmates that the situation is really delicate ... inside the jail. It is has [also] become very tense in the capital," said our correspondent.
Yemen has been rocked by protests inspired by recent uprisings in Egypt and Tunisia that ousted those nations' leaders.
Many protesters are angry at widespread corruption in a country where 40 per cent live on $2 a day or less and where university graduates without connections struggle to get jobs. Youth unemployment is rampant.
Yemen is also riven with regional strife, with Shia rebels in the north and separatists in the south demanding fairer political participation.