Thousands of protesters backed by military defectors seized a base of the elite Republican Guards on Monday, weakening the control of Yemen’s embattled president over this poor, fractured Arab nation. His forces fired on unarmed demonstrators elsewhere in the capital, killing scores, wounding hundreds and sparking international condemnation.

The protesters, joined by soldiers from the renegade 1st Armored Division, stormed the base without firing a single shot, according to witnesses and security officials. Some carried sticks and rocks. They used sandbags to erect barricades to protect their comrades from the possibility of weapons fire from inside the base, but none came and the Republican Guards eventually fled, leaving their weapons behind.

Although the base was not particularly large — the Republican Guards have bigger ones in the capital and elsewhere in Yemen — its capture buoyed the protesters’ spirits and signaled what could be the start of the collapse of President Ali Abdullah Saleh’s 33-year-old regime.

“It was unbelievable,” said protester Ameen Ali Saleh of storming the base on the west side of the major al-Zubairy road, which runs through the heart of Sanaa. “We acted like it was us who had the weapons, not the soldiers.”

“Now the remainder of the regime will finally crumble,” said another demonstrator, Mohammed al-Wasaby. “Our will is more effective than weapons. The soldiers loyal to Saleh just ran away.”

As clashes continued into the night, several loud explosions rocked Sanaa, and a mortar hit the Islamic University of Al-Iman, killing one and injuring two others. The cause of the explosions was not known.

Saleh went to Saudi Arabia for medical treatment after a June attack on his Sanaa compound and has not returned to Yemen, but has resisted calls to resign.

A final showdown may well pit the Republican Guards, led by Saleh’s son and heir apparent Ahmed, against the soldiers of the 1st Armored Division, another elite outfit that has fought in all of Yemen’s wars over the past two decades, and their tribal allies in the capital.

The Republican Guards and the Special Forces, also led by the president’s son, have long been thought to be the regime’s last line of defense against the seven-month-old uprising.

The storming of the base capped two days of clashes in the capital that have left at least 50 people dead and nearly 1,000 injured, mostly demonstrators.

Government forces used snipers stationed on rooftops, anti-aircraft guns, rocket propelled grenades and mortars against the unarmed protesters. Witnesses and security officials described scenes of mutilated bodies, some torn apart. An infant girl, a 14-year-old boy and three rebel soldiers were among the at least 23 people killed on Monday.

“It is over,” concluded protest leader Abdul-Hadi al-Azzai. “The Ali Abdullah Saleh regime is finished. How can you negotiate while massacres are ongoing? The world is silent.”