MOSCOW, October 17 (RIA Novosti) - Pakistan forces began on Saturday an offensive against Taliban militants in the country's South Waziristan area, regional media said.

Some 30,000 to 40,000 troops are taking part in a ground and air operation. Fierce fighting is reported to have broken out and local officials have reported casualties. Pakistani authorities imposed a curfew in the area before the attack was launched.

The assault against the Pakistan-based Taliban, led by Hakimullah Mehsud, comes after days of militant violence across the country, in which up to 150 people have died.

The United Nations said on Friday that some 250,000 residents had fled the area ahead of the offensive. Refugee numbers are expected to rise as the fighting continues.

The attack has been expected since June 15, when the governor of the North West Frontier Province announced a ground offensive.

U.S. President Barack Obama signed legislation on Thursday providing Pakistan with $7.5 billion in aid over the next five years. Some of the funds are conditional on Pakistan fighting Taliban militants.