Shelling by Yemen's Republican Guards wounded at least four people during clashes with opposition tribesmen in the southern city of Taez, tribal sources said on Friday.
The fighting broke out on Thursday night between the Guards loyal to embattled President Ali Abdullah Saleh and tribesmen allied with demonstrators who have since January called for him to quit, the sources said.
The shelling was especially focused on Al-Rawda and Osaifra neighbourhoods and continued until Friday morning.
Witnesses said there was widespread panic.
Anti-regime activists have appealed for protests under the slogan "Friday of a Civil State," after a call from influential cleric Sheikh Abdel Majid al-Zindani for the establishment of an Islamic state.
Supporters of Saleh have meanwhile called for demonstrations of "Thanks and gratitude to the Custodian of the Two Holy Mosques," in reference to King Abdullah of Saudi Arabia, where Saleh has been hospitalized for more than a month after being wounded in a bomb attack on his palace.