Hundreds of thousands of Yemenis are demonstrating to demand President Ali Abdullah Saleh face trial for his regime's deadly crackdown on months of protests.
Sunday's rallies are taking place in the capital, Sanaa, and other cities.
After months of pressure, Saleh signed a deal last month to step down as president in exchange for immunity from prosecution. New presidential elections are set for Feb. 21.
The deal has failed to end the protests, which began last February with calls for his ouster. Protesters also rejected a unity government formed over the weekend that includes some ministers from Saleh's administration.
In part of the capital where armed tribesmen have battled Saleh's forces, five explosions were heard early Sunday. A medic said two people were injured.