CAIRO (Reuters) - Fifteen militants were killed in the Sinai Peninsula by rocket fire, Egyptian state TV reported on Tuesday, after witnesses said army helicopters had attacked militant strongholds in the area.

The state-run Nile TV gave no further details in a brief report. The army helicopters had targeted two villages south of Sheikh Zuweid, a town near the border with Israel and the Hamas-run Gaza Strip.

An army source said a ground operation was under way with air cover, but declined to give further details because it was still continuing.

Security sources said government helicopter strikes had killed at least eight armed men and wounded 15, and had been aimed at stores of arms and explosives in the Sinai.

Militant attacks on security forces in the lawless North Sinai region have risen since the army, prompted by mass protests, ousted Egypt's first elected Islamist president, Mohamed Mursi, on July 3.

Growing insecurity in Sinai worries the United States and others because the region is bounded not only by Israel and the Gaza Strip but also by the Suez Canal, a major global shipping artery.

Last Saturday, attackers fired at a ship passing through the Canal.