The Republican Guard force led by President Ali Abdullah Saleh’s son attacked the protesters as they converged on the capital after a four-day march from the southern city of Taiz, a center of the opposition.
Participants in what has been dubbed the March of Life followed a 170-mile (270-kilometer) route.
The lengthy march, a first in the 10 months of demonstrations, aimed to pressure a new national unity government and parliament to reject the immunity deal for Saleh.
One of the organizers, Abdel Nasser Aal-Kamali, says 30 people were injured in Saturday's attack.
Yemeni troops defied orders to withdraw from the streets of the capital by a Saturday deadline, signaling trouble for a deal meant to ease the president from power and end months of protests.
The Republican Guard force and the Central Security forces led by Saleh's nephew could still be seen throughout Sanaa on Saturday, after the deadline passed. As a result, anti-Saleh forces from a renegade army battalion as well as armed tribesmen opposed to the president have also stayed put.
The deal signed last month by Saleh and several opposition parties is aimed at bringing an end to the authoritarian ruler’s 33 years in power.
Street protesters, however, are refusing to end rallies because they object to part of the deal granting Saleh immunity from prosecution over the killings of demonstrators in the uprising, which began in February.
Yemen’s parliament convened Saturday for the first time since opposition and independent lawmakers suspended their participation in March to protest the crackdown. Lawmakers were to discuss the program of the new national unity government, headed by veteran independent politician Mohammed Basindwa.
On Dec. 7, Basindwa said the government will focus on providing public services to the people, including electricity, water, fuel and basic commodities together with restoring security and stability.
Services and security have been in short supply during the unrest in Yemen, the poorest country in the Arab world.
