At least 56 protesters were killed in clashes in Yemen's capital of Sanaa on Teusday, agencies report.
The violence came as Yemeni president Ali Abdullah Saleh met with King Abdullah of Saudi Arabia in Riyadh amid reports a Gulf-brokered transfer of power deal will be signed in days.
As the meeting drew near, thousands protesters in Sanaa, reinforced by army defectors, laid seige to a military installation in the capital held by members of the Republican Guard.
Entrenched defenders used live fire to repel protesters armed with rocks and clubs in a pitched battle lasting hours before finally withdrawing when it became appaerent reinforcements would not arrive.
The base is not the only or largest military installation in or near the capital, but its violent seizure raises concerns violence may spread even as strides are being made to end months of unrest in the country.
The violence was escaberated when soldiers of General Ali Moshen, who defected after a brutal crackdown in March, exchanged heavy fire with the soldiers holding the besieged installation.
Rocket fire was also exchanged in the clash between Moshen's forces and government soldiers, with at least two stray rockets hitting a field hospital where protesters wounded in the clash.
The government reportedly deployed snipers during the chaos, whose fire was described as "slaughter" by witnesses.
Yemen's opposition movement has refused to believe president Ali Abdullah Saleh is serious about relinquishing power and vowed to keep the pressure on until he goes.
The protesters frustration and confrontationsal posturestems from Saleh backing out of a deal brokered by the six-member Gulf Cooperation Council (GCC) three times previously.
However, critics say say this time the circumstances are different and the violent protest was an irresponsible move that led to unecessary bloodshed.
Saleh announced last week he will not return to Yemen from Saudi Arabia, where he has been recovering from wounds sustained in an assasination attempt in june, and authorized his vice president, Ali Muhammed Mujawar, to sign the Gulf-brokered transfer of power agreement in his stead.
Officials in Riyadh and Washington, as well as their envoys trying to stave off more violence in Sanaa, say they expect that signature within days - ending Saleh's 33-year rule.
Sources: AP, Reuters, and Gulf News.