The foreign institutional investors (FIIs) were net sellers to the tune of Rs 659.74 crore in the futures & option segment on Tuesday.According to data released on the NSE website, FIIs were net sellers of index futures to the tune of Rs 645.05 crore while they bought index options worth Rs 27.39 crore. They were net sellers of stock futures to the tune of Rs 51.62 crore and they bought stock options worth Rs 9.54 crore.As per data available on the Sebi website - FIIs were net buyers of stocks worth Rs 21.90 crore in the spot market on Monday. Domestic mutual funds (MFs) were net sellers of shares worth Rs 52.66 crore on the same day.