Police said the incident took place on the Yamuna Expressway Sunday evening. The students were accused by the tour operator of making lewd gestures and eve teasing. District Magistrate Zuher Bin Sagir said it was a serious matter. 

The tour operator alerted the Etmauddaula police station after he failed to persuade the students to mind their own business and not indulge in making lewd gestures and scaring the American girls.

The students in their car followed the bus from the Jevar toll plaza. A few of them climbed into the bus, while some others parked the car in front of the vehicle.

"The girls were frightened," tour operator Anil told police. Police said the students are from Rohini and Patel Nagar in Delhi.