More than 20,000 Yemenis filled the streets of Sanaa on Thursday for a "Day of Rage" rally, demanding a change in government and saying President Ali Abdullah Saleh's offer to step down in 2013 was not enough.
Further anti-government protests were expected across Yemen, which Saleh has ruled for over three decades, and supporters of the president were driving around the capital urging Yemenis over loudspeakers to join pro-government counterdemonstrations.
But by early morning, anti-government protesters had already gathered the largest crowd since a wave of protests hit the Arabian Peninsula state two weeks ago, inspired by protests that toppled Tunisia's ruler and threaten Egypt's president.
"The people want regime change," protesters shouted as they gathered outside Sanaa University. "No to corruption, no to dictatorship."
Saleh, eyeing the unrest spreading in the Arab world, indicated on Wednesday he would leave office when his term ends in 2013, and promised his son would not take over the reins of government, among a host of other political concessions.
It was his boldest gambit yet to stave off turmoil in Yemen, a key ally of the United States against al Qaeda, as he sought to avert a showdown with the opposition that might risk sparking an Egypt-style uprising in the deeply impoverished state.
Wael Mansour, an organiser of the Thursday rally, said Yemenis were not satisfied with Saleh's concessions.
"Today will bring more, fresh pressure on President Saleh, who will have to present further concessions to the opposition," he said, without specifying what those concessions might be.
The risks are high for Yemen, on the brink of becoming a failed state, as it tries to fight a resurgent al Qaeda wing, quell southern separatism, and cement peace with Shi'ite rebels in the north, all in the face of crushing poverty. One third of Yemenis face chronic hunger.
The United States relies heavily on Saleh to help combat al Qaeda's regional Yemen-based arm which also targets neighbouring Saudi Arabia, the world's biggest oil exporter. Instability in Yemen would present serious political and security risks for Gulf states.
U.S. President Barack Obama telephoned Saleh to express support for his initiative, the state news agency Saba said. "You have handled the situation well, and I look forward to working with you in a good partnership between the two countries," it quoted Obama as saying.