The four were taken into custody yesterday while they were trying to pull down barbed wires surrounding the plot, a disputed property, SSP, Aligarh, Piyush Mordia, said.
Eyewitnesses said the four fired in the air to scare off the students gathered to stop them, and had come in vehicles bearing Samajwadi Party flags.
The four belong to the neighbouring districts of Moradabad and J P Nagar, Mordia added.
A spokesman for AMU said the institution's Vice Chancellor today asked that all relevant facts pertaining to the incident be placed before him.