Foreign institutional investors (FIIs) were net sellers of Rs 673.40 crore on Tuesday, December 19, according to data released by Sebi today.While FIIs made gross purchases of Rs 1,580.10 crore, gross sales totalled Rs 2,253.50 crore.Mutual funds (MFs) were net buyers of Rs 10.69 crore on Tuesday. MFs made purchases of Rs 663.79 crore and sales of Rs 653.10 crore.