CAIRO, Sept 19 (Reuters) - An Egyptian police officer was shot dead on Thursday, state media reported, in clashes on the outskirts of Cairo as security forces tried to reassert control over an area where 11 policemen were killed in a militant attack last month.

Police and soldiers entered the town of Kerdasa at daybreak in the second operation this week to try to restore control over Islamist-dominated areas where hostility to the authorities has grown since the army deposed President Mohamed Mursi on July 3.

Security sources said the forces had seized dozens of weapons, including rocket propelled grenades. The police officer, a general, was killed in an exchange of gunfire on the outskirts of the town. Fifteen people had been arrested.

State television reported that security forces used tear gas and the state news agency said army helicopters hovered overhead. Police were hunting 140 wanted people, the Interior Ministry spokesman told state media.

"The security forces will not retreat until (Kerdasa) is cleansed of all terrorist and criminal nests," said the spokesman, Hany Abdel Latif.

Footage broadcast by the privately-owned Mihwar TV channel showed armoured personnel carriers, police and soldiers in the streets.

There had been little or no sign of state authority in Kerdasah since an Aug. 14 attack on its police station, which was hit with rocket propelled grenades and torched as police broke up protests by Mursi supporters in Cairo.

Churches were also attacked.

Hundreds of Mursi supporters were killed on Aug. 14, when the security forces moved against the pro-Mursi protest camps in Cairo, setting off the worst spasm of violence in Egypt's modern history.

In a similar operation earlier this week, the security forces moved into the town of Delga in the southern province of Minya - scene of some of the worst violence last month. Around 70 people were killed and about 20 churches torched in Minya.

At least 2,000 people, mostly Mursi supporters, have been arrested since Mursi's ouster, and more than a hundred members of the security forces have been killed.

Kerdasah, known for producing fabrics, is 14 km (9 miles) from Cairo. (Reporting by Ali Abdelatti, Yasmine Saleh; Writing by Tom Perry, editing by Elizabeth Piper)