Manchester United and Real Madrid have been involved in a row over their summer tour arrangements after both clubs picked the same city for their preseason base, sources have told ESPN FC.

The heavyweights have been butting heads over everything from hotels to training pitches in Los Angeles as club officials have tried to plan their trips.

The relationship between United and Real Madrid became so fractured ahead of the International Champions Cup that tournament chiefs and promoters Relevent Sports have been forced to step in.

It is the latest instalment of a long-running feud. The pair have been locked in a battle over the services of goalkeeper David De Gea while this summer United unexpectedly called off negotiations over striker Alvaro Morata after announcing a deal for Romelu Lukaku.

United won the battle over facilities in L.A. after securing the Beverly Wilshire and Montage as their team hotels, the same accommodations they used for Louis van Gaal's first tour as manager in 2014. They are also using the bigger training pitches at UCLA, closer to the changing rooms.

Their hotel is also equipped with an outside swimming pool for players to use with temperatures on the West Coast of America reaching record heights this week.

Importantly for United coach Jose Mourinho, the pitch at Drake Stadium on the UCLA campus is more private than the one Real Madrid have been forced to use just a few yards away.

United arrived in L.A. on Sunday and held an open training session on Monday morning. Sessions on Tuesday, Wednesday and Thursday this week have been closed off to the media.

Real Madrid, who are staying at the Beverly Hills Hotel, arrived on Tuesday. United and Real are due to meet twice this summer.

They are set to meet at Levi's Stadium in Santa Clara on July 23 before going head-to-head again in the UEFA Super Cup in Macedonia on Aug. 8.

On Wednesday night, a bomb threat led hundreds of students to seek refuge at Drake Stadium, just hours after Mourinho's men finished training.

After someone called in a bomb threat to the college's recreation center, students evacuated their residence halls, but the Los Angeles Times reported that after two hours, police determined the threat was unfounded.

A UCLA spokesman told the newspaper that more than a dozen residence halls and the recreation center were evacuated and students gathered at Drake Stadium, where United had trained earlier in the day. Students in other areas of the campus were told to remain indoors.

A security team follows Mourinho's side around the city, just as they do elsewhere on their travels, and UCLA security presence is visible around Drake Stadium.