Six people killed and scores of others injured by security fire in Sana'a, Al Arabiya reported.
Sunday's violence, jolting an uneasy, weeks-long stalemate, was the worst in recent months. Hundreds of people in an anti-government march were wounded as well when security forces fired on protesters who charged police lines.
Opposition organizers called for more action on Monday, rousing sleeping protesters who have been camped in Sanaa's Change Square for eight months to demand an end to 33 years of autocratic Saleh rule in impoverished Yemen.
Shouting over loudspeakers, organizers urged protesters to head back to a junction they had taken on Sunday night, known locally as Kentucky roundabout, and hinted they planned to push further into territory held by government forces.
The area had previously marked the dividing line between the parts of Sanaa held by loyalist troops and defected forces, Reuters reported.