LONDON (AP) — As the Manchester City team bus made its way out of Anfield, there came a parting shot.

An object, supposedly thrown by home fans after the bad-tempered 1-0 loss to Liverpool on Sunday, caused a small crack in the windshield.

It’s a rivalry that has turned ugly, the bitterest in the Premier League.

City manager Pep Guardiola had already successfully avoided coins being hurled in his direction during the match. Liverpool, meanwhile, condemned the behaviour of the away fans after offensive chants relating to Hillsborough — the tragedy in 1989 that resulted in the deaths of 97 of its fans.

As fierce as the competition has been on the field during a four-year period when the teams have dominated English soccer, so has the feud been off it. A person with knowledge of the bus incident said City will make an official complaint to the English Football Association.

The person spoke on condition of anonymity because City has yet to publicly comment on the events surrounding the match. The coin-throwing and Liverpool manager Jurgen Klopp’s pre-match comments will also be included in the complaint, the person said.

“There are three clubs in world football who can do what they want financially,” Klopp said on Friday, an apparent reference to City, Paris Saint-Germain and Newcastle, who are backed by Abu Dhabi, Qatar and Saudi Arabia, respectively.

Tensions between the clubs have been building for some time — dating back to before their recent battle for supremacy at the top of the Premier League.

Raheem Sterling’s transfer to City in 2015 pointed to a shift in the balance of power from one of European soccer’s traditional giants to its newly-enriched rival, which was bought by the Abu Dhabi royal family in 2008. As a result, the England forward was heavily-criticized for what was perceived as a financially motivated move.

“Trophies don’t get handed out, you’ve got to earn them,” former Liverpool defender Jamie Carragher said at the time. “You’ve got to deliver in big games and he hasn’t done that yet.”

Sterling went on to win four titles at the Etihad Stadium and 10 major trophies.

But the rivalry really intensified when Klopp emerged as the greatest threat to Guardiola’s dominance.

Liverpool beat City in three-straight games in the second half of the 2017-18 campaign, which saw Guardiola’s team crowned champion with a record 100 points.

It was a notice of intent from Klopp, while Liverpool fans appeared determined to intimidate City, not only with the famously daunting atmosphere inside Anfield, but also by attacking the visiting team bus ahead of a Champions League quarterfinal match.

The damage caused was so severe that a replacement bus was required to get the team back to Manchester.

The small crack left on the windscreen on Sunday was not as dramatic, but it was the latest incident involving two teams that have set standards on the field that have not been matched by their fans off it.

Liverpool said it wants to work with City to eradicate “vile chants.”

“The concourse in the away section was also vandalized with graffiti of a similar nature,” Liverpool added in a statement after Sunday’s match.

Meanwhile, Klopp, who was sent off for angrily charging out of his technical area to remonstrate with the referee’s assistant, apologized for the coin-throwing.

“Horrible,” he said. “I am sorry. It never should happen.”

How the FA unpicks a game that was overshadowed by flash points off the field is not straight-forward. It has limited jurisdiction over isolated incidents of objects being thrown from the crowd from individuals. And while it has condemned the chants from City fans, it would only normally act when discrimination is involved.

Klopp’s fate is also uncertain.

The Liverpool manager won’t face an automatic suspension for his red card, the FA said. The governing body will review the incident before deciding whether to offer him a ban and/or a fine. If his behaviour is deemed to be serious enough, he could face a hearing and potentially more severe punishment.

If the fall-out from this latest engrossing clash between City and Liverpool has shown anything, it’s that this rivalry isn’t going away any time soon.

___

AP World Cup coverage: https://apnews.com/hub/world-cup and https://twitter.com/AP_Sports

___

James Robson is at https://twitter.com/jamesalanrobson