Several large explosions shook an air base outside the Yemeni capital, Sana'a, prompting authorities to temporarily close the city's nearby international airport Sunday.
Yemeni authorities said mortar shells landed at the al-Daylami air force base, a few kilometers from the airport, causing a massive blast and sending up huge plumes of smoke.
Flights were temporarily rerouted from Sana'a International Airport to the southern port city of Aden.
There were no immediate reports of casualties. CNN quotes a Yemeni government official as saying the base was shelled by opposition forces.
Earlier Sunday, Yemeni tribal and security sources said forces loyal to President Ali Abdullah Saleh shelled a residential area north of the capital, killing four civilians - three of them children - and wounding 12 other people.
The incident took place in the Arhab district, a stronghold of Yemeni tribesmen who support a months long opposition uprising against Mr. Saleh's 33-year rule.
Elsewhere, medics and witnesses said one civilian was killed by sniper fire in the southern city of Taiz. The area has seen frequent battles between pro-Saleh forces and opposition tribesmen.
Also Sunday, a bomb destroyed a police vehicle on patrol in Aden, killing one officer and wounding three others. Officials said suspected militants 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.