Witnesses and medical officials in the Yemeni capital, Sana'a, say shelling in the city has killed two civilians.

The witnesses said the mortar fire Tuesday wounded at least one other person when the shells fell on a market.

It was not clear who fired the mortars.

Government troops have been fighting followers of tribal leader Shekh Sadek al-Ahmar and opposition fighters led by rebel General Ali Mohsen al-Ahmar. The clashes in the capital have escalated in recent weeks.

President Ali Abdullah Saleh said last week he will not step down as long as the general and another key rival retain power and influence in the country. He accused his political rivals of hijacking Yemen's popular revolt in order to force him from office.

Mr. Saleh returned to Sana'a in late September after a three-month stay in Saudi Arabia to recuperate from a June attack on his palace.