Barcelona condemned the actions of fans who mobbed under-fire manager Ronald Koeman's car as he left Camp Nou after a 2-1 defeat to Real Madrid in the first Clasico of the season.

Goals from David Alaba and Lucas Vazquez put Madrid into the lead and Sergio Aguero's stoppage-time strike proved merely a consolation as Barca slipped to a fourth consecutive Clasico defeat – the last three coming under Koeman.

The Dutchman is only the second Barca manager in history to lose his first three LaLiga games against Real Madrid, with Patrick O'Connell having suffered the same fate between 1935 and 1940.

With Barca ninth in LaLiga and third in their Champions League group, pressure is mounting on Koeman as fans grow restless with the team's poor performances.

That unrest spilled over in the aftermath of the loss against Los Blancos, with a crowd of fans mobbing Koeman's car as he left the stadium.

Barca released a statement to deplore those actions and vowed to increase security in order to prevent a repeat.

"FC Barcelona publicly condemns the violent and disdainful acts that our manager experienced when leaving the Camp Nou," the statement read. 

"The club will take security and disciplinary measures so that such unfortunate events do not happen again."

Barcelona travels to seventh-placed Rayo Vallecano on 27 October and will hope to bounce back from its demoralising defeat.