Yemeni tribal and security sources say government forces have shelled a residential area north of the capital, Sana'a, killing four civilians, three of them children.

The tribal and security officials say troops loyal to President Ali Abdullah Saleh fired artillery into a gas station in Arhab district on Sunday, killing the civilians and wounding at least 12 other people. Arhab is a stronghold of Yemeni tribesmen who support a 10-month-old opposition uprising against Mr. Saleh's 33-year rule.

Elsewhere, medics and witnesses say one civilian was killed by sniper fire in the southern city of Taiz on Sunday. Taiz has seen frequent battles between pro-Saleh forces and pro-opposition tribesmen.

In other violence Sunday, security officials say a bomb destroyed a police vehicle on patrol near the airport in the southern port of Aden, killing one officer and wounding three others. The officials say suspected militants had planted the bomb inside the vehicle.

Yemeni security forces frequently come under attack in the country's south, where Islamist militants linked to al-Qaida seized control of several towns earlier this year.