Police made seven arrests after crowd trouble marred West Ham's 2-1 win over Chelsea in the EFL Cup on Wednesday.
The fixture, typically played in a fraught atmosphere between London rivals, was subject to heavy stewarding and policing.
But problems developed late in the game, as stewards battled to maintain segregation between the two sets of fans with Chelsea 2-0 down.
A Metropolitan Police statement read: "Although the vast majority of people left the stadium peacefully and were well behaved, there were a minority of people who attended the match that were clearly intent on being involved in confrontation and violence.
"Despite extensive work with both clubs and the London Stadium partners as well as a large and robust policing operation, there were unacceptable incidents inside and outside the stadium, before, during and after the game.
"We welcome the condemnation from partners and have already started a post-match investigation.
"We have already made seven arrests and will work tirelessly to identify people involved and bring them to justice."
West Ham "unreservedly" condemned the actions of sections of supporters swiftly after the game.
Previous incidents at matches against Watford and Middlesbrough - along with poor performances on the pitch - have made for a difficult start to life at London Stadium for West Ham, having left Upton Park at the end of last season.