West Ham co-owner David Sullivan has criticised police and stewards at London Stadium after fan protests during Saturday's 3-0 defeat against Burnley spilled over to a shocking extent.
Fans invaded the pitch after Burnley's second-half goals, with one wrestled to the ground by Mark Noble after confronting the West Ham captain, while another individual planted a corner flag in the middle of the pitch.
A separate group of supporters congregated below the directors' box and directed their anger towards Sullivan and fellow owner David Gold, who were ushered from their seats as a safety precaution.
West Ham issued a statement after the match, pledging a "full and thorough investigation" into how events deteriorated to such a staggering extent, but Sullivan has already apportioned a degree of the blame.
"We feel very badly let down by the stadium operators appointed by the [London] Mayor's staff," he told Mirror Sport.
"Where were the stewards and police?"
The Premier League strongly condemned the incidents at the site of the London 2012 Olympics, while the Football Association will seek observations from West Ham and the match officials.
A number of videos circulated on social media, appearing to show one steward dozing off at his post, while two fans invaded the pitch and were able to return to their seats before being escorted out.
David Moyes' side are 16th in the Premier League, three points above the relegation zone, after losing four of their past five matches and face fellow strugglers Southampton at home in their next top-flight game on March 31.
A number of Hammers fans were due to march against the board on Saturday, but the protest was cancelled at the last minute.
The club has been engulfed in toxicity in recent months, with results on the slide and the supporters angered by a lack of investment from the board, as well as the lingering bad feeling over the move to the London Stadium from Upton Park.