Manchester City manager Pep Guardiola questioned the organisation of his side's arrival at Anfield after City's team bus was pelted by bottles and cans ahead of their highly-charged Champions League quarter-final at Liverpool on Wednesday.

Liverpool were forced to apologise after windows were broken and two police officers injured by missiles thrown ahead of Liverpool's 3-0 win.

Guardiola was warned about the hostile reception his side would receive in his pre-match press conference on Tuesday, and queried why more protection wasn't offered to his players.

"Yesterday you (the media) explain about that, but I am new here for the Champions League. You explained about that is going to happen and it happened," said the Catalan coach.

"Normally when the police know that is going to happen it is to try and avoid it happening."

Guardiola also suggested more protection should be given to team buses in general with this latest attack coming a year after a bomb attack on Borussia Dortmund's bus ahead of their Champions League quarter-final against Monaco.

"One year ago something happened in Dortmund. We come here to play football, it is sport, and I don't understand this kind of situation," added Guardiola.

"The bus is destroyed. But I don't expect this from Liverpool, such a prestigious club, to do this sort of things.

"Of course is not liverpool, it is the people, but hopefully it doesn't happen again."

Liverpool supporters surrounded the roads around Anfield and let off flares in a frenzied atmosphere for the club's first Champions League quarter-final in nine years.

The bus was reportedly rendered unusable by the damage and City sent for another for the short 55km (35-mile) journey home.

Liverpool swiftly issued a statement of their own pledging to identify the culprits.

"The club condemns in the strongest possible terms the scenes which preceded our Champions League quarter-final, which resulted in damage being inflicted on the Manchester City team bus during their arrival at Anfield," the statement read.

"We apologise unreservedly to Pep Guardiola, his players, staff and officials caught up in the incident.

"The behaviour of a number of individuals was completely unacceptable and the club will cooperate fully with the authorities to identify those responsible.

"The priority now is to establish the facts and offer Manchester City whatever support is necessary."

Liverpool manager Jurgen Klopp also apologised, saying: "I really don't understand it. We tried everything to prevent a situation like that. For Liverpool FC I have to say sorry."

Merseyside Police said they would launch enquiries to find the culprits of what they described as "appalling" behaviour.

"Thankfully no one on the bus was injured, but injuries were caused to two of our officers when projectiles were thrown towards the bus," said match commander superintendent Paul White in a statement.

"This behaviour by a number of people who threw bottles, cans and pyrotechnics towards the bus is completely unacceptable and we will conduct enquiries to identify who was responsible and bring them to justice.

"We worked very closely with both clubs to ensure the safety of the public and the teams themselves, and it is disappointing to see that a number of people behaved in this appalling way."