Government forces in southern Yemen killed 12 al-Qaida-linked militants and wounded three others in shelling attacks Sunday, officials said.
They said the shelling was concentrated on the Dufas area in Zinjibar, capital of Abyan province. Eight soldiers were wounded in the fighting, according to the military hospital.
Militants are taking advantage of internal strife in Yemen to overrun parts of the country.
A senior military official said the shelling was meant to clear way for the armed forces to retake the city. The Islamic militants used to counterattack in night raids but have not hit back for three days, the official said.
The official said that the Islamic militants planted land mines on the front lines to prevent the army from advancing.
All the officials spoke on condition of anonymity because they were not authorized to brief reporters.
Local authorities closed the highway that links Aden to Abyan to prevent civilian causalities.
Several days ago, warplanes attacked militant hideouts, killing several fighters. The government also shelled the areas.
In response, the Ansar al-Sharia group listed in a statement the names and ranks of 12 air force and army officers it said it intended to kill for taking part in the attack.
Hundreds of residents of the city of Zinjibar have fled their homes, searching for safe villages in the countryside.
Ali Dahmas, a resident, said that until now the army has not taken decisive measures against the militants. He said, "Until the political instability in Yemen comes to an end, we will suffer from those Islamic extremists."
Opponents of President Ali Abdullah Saleh charge that he has allowed the Islamic militants to take over southern cities to show that al-Qaida related militants will gain if he is forced from power.
"The authorities have to prove that they are not collaborating with these groups," Dahmas said.
Saleh is being treated in Saudi Arabia for serious injuries suffered in a June 3 attack on his palace. In his absence, Yemen's opposition parties have sought to persuade the ruling party to join them in a transitional leadership that would effectively shut out Saleh, who has resisted pressure at home and abroad to step down.
Yemen's political turmoil began with anti-government protests in February. The country is the poorest in the Arab world, suffers numerous internal conflicts and is a potential source of instability for neighboring Saudi Arabia and other oil-rich parts of the Arabian peninsula.
For the U.S. and Europe, the main concern is the al-Qaida offshoot that has found refuge in Yemen's mountainous hinterlands and has been behind several nearly successful strikes on U.S. targets.