Restaurant customers fled as members of the Bajrang Dal raided the restaurant in Thane, but there were no reports of injuries, police said. In southern Bombay, another McDonald's was surrounded by demonstrators from the ruling Bharatiya Janata Party, who shouted slogans and smeared cow dung.
McDonald's says it does not use any animal extracts in its French fries in India, where the cow is considered sacred by most Hindus. But it confirmed it uses some beef flavoring, though not beef fat, in its American fries.
The Shiv Sena, another Hindu group, said it would protest outside the corporate office of McDonald's in India on Saturday.
The protests were touched off by front-page newspaper reports about a lawsuit filed in Seattle on Tuesday.
An Indian-American lawyer accused McDonald's of using beef fat in the preparation of French fries more than a decade after it said it would cook its fries in vegetable oil.
Most of India's Hindus - 85 percent of the population - are vegetarians, although with urbanization more Indians are becoming meat eaters.
McDonald's Corp. in the United States announced in 1990 that its restaurants would no longer use beef fat in making French fries and that only pure vegetable oil would be used.
The fast-food chain released a statement Wednesday saying it has never claimed the fries it sells in the United States are vegetarian. The statement said the recipe for the fries uses a ``a minuscule trace of beef flavoring, not tallow.''
Tallow is shortening made from beef fat.
McDonald's India, which opened its first restaurant in India in October 1996, now has 28 outlets in New Delhi, Bombay, Pune, Jaipur and on the Delhi-Agra highway.