Police tried to disperse the demonstrators using tear gasand batons, but about 3,000 protesters defiantly continuedtheir march from Sanaa University toward the city centre,chanting slogans against President Ali Abdullah Saleh,including "Down with the president''s thugs!"
The procession gained momentum with hundreds of studentsand rights activists joining along the way.
The unrest comes as ties between the US and Saleh havebeen growing recently over rising alarm in Washington aboutthe activities of al-Qaida in the Arabian Peninsula.
The US military has embarked on a plan to deepen itsinvolvement in training Yemen''s counterterrorism force tocounteract a local affiliate of al-Qaida that has mountedseveral attacks against the US.
Saleh, who has been in office for more than 30 years, hastried to blunt recent unrest by promising not to seekre-election when his term ends in 2013.
He has been contacting powerful tribal leaders in a bidto enlist their support as he attempts to defuse the protests,according to officials familiar with the president''s moves.
They spoke on condition of anonymity because of thesensitivity of the subject.
The officials said Saleh feared that his rule would notwithstand the pressure of a tribal decision to join theprotesters in seeking his ouster.
For now, said the officials, Saleh was counting on thesecurity forces and armed backers who support his rule indealing with the protesters.
Today, riot police blocked the main road leading to thecity center and clashed with protesters throwing stones. Threeprotesters were injured and taken to the hospital inambulances.
About 2,000 government supporters staging acounterdemonstration joined the police in battling theprotesters.
"We will not back off, whatever the government thugs do,"said Tawakul Karman, a senior member of the opposition Islamicfundamentalist Islah Party, She was briefly arrested lastmonth for leading anti-government protests.
"We will retain the dignity of the people and theirrights by downing the regime," she added. Rights activistFathi Abu al-Nassr called the demonstrations "the people''suprising." (AP)