KOLKATA, India, Feb 15 (Reuters) - About 100 Maoist rebels, many riding motorcycles, stormed a police camp in eastern India on Monday and killed at least 15 policemen as they fired indiscriminately and set fire to the site. Police said the ambush was on a camp in the state of West Bengal, 200 km (125 miles) west of the state capital Kolkata, in the same area where a major anti-Maoist offensive was launched last year.