"We have come to know from social media that some supporters wearing Mohun Bagan jerseys have brought down the overhead gate which was erected by East Bengal to commemorate their centenary celebrations. We condemn this nasty and unethical behaviour in the strongest of words," Mohun Bagan said in a statement.
The green and maroon brigade management added that they will bear the entire expense required to re-erect the gate.
"We have sent a letter to Kalyan Majumder, General Secretary of East Bengal Club, condemning the act and have requested them to re-erect the gate, the cost of the same will be borne by us.
"Further, we have also lodged a complaint at the Maidan police station to take appropriate action as per law. Our Finance Secretary Debashis Dutta had personally called Debarata Sarkar to condemn the act.
"We once again condemn such act and appeal to supporters of both the clubs to maintain mutual respect and harmony so that the image of the clubs and football are not tarnished," the statement added.
A social media video which went viral on Twitter showed some persons wearing the Mohun Bagan club colour bringing down the East Bengal gate with its centenary logo on it.
Bystanders were seen watching the incident unfold in front of their eyes.
East Bengal recently kickstarted their centenary celebrations on their Foundation Day on August 1 by awarding cricket legend Kapil Dev with the Bharat Gaurav award, East Bengal's highest honour.
Besides Kapil, a galaxy of stars including soccer stars Bhaichung Bhutia, Sunil Chhetri, former India skipper Sourav Ganguly, actor Soumitra Chatterjee and West Bengal Chief Minister Mamata Banerjee were present on the occasion.
( With inputs from IANS )