The 29-year-old Sanchez, who was out of contract at Arsenal at the end of the season, has joined the Old Trafford club after local rivals Manchester City had pulled out of the race.

British media reported that Alexis Sanchez, who will wear United's iconic No. 7 shirt, has joined the club on a 4-1/2-year deal, while Arsenal announced that Armenia captain Mkhitaryan, who turned 29 on Sunday, had signed a long-term contract.

Read: Arsenal`s Alexis Sanchez Likely to Join Man United: Wenger

Sanchez said, "I am thrilled to be joining the biggest club in the world. The chance to play in this historic stadium and to work with Jose Mourinho was something I could not turn down.

"I am very proud to be the first Chilean player ever to play for United’s first team and I hope I can show our fans all around the world why the club wanted to bring me here."

Sanchez missed Arsenal's 4-1 win over Crystal Palace on Saturday to have a medical in Manchester on Sunday.

Alexis Sanchez would have been available on a free transfer when his contract expired in four months' time but once City balked at the amount of money involved in a mid-season deal, Manchester United manager Mourinho urged his club to step in.

REUTERS