The 54-year-old Argentine was officially appointed by United following the dismissal of Michael Carrick, bringing an end to his two-year spell in charge of the USA. Pochettino had signed a four-year contract extension in August, committing himself to the national team until the 2030 World Cup.

"We learned a lot from you all, from this amazing country," Pochettino told reporters on Friday. "I think this was one of the most difficult decisions of (my) career."

The former Tottenham, Chelsea and Paris Saint-Germain manager became emotional as he thanked the players and staff for their contribution, admitting that walking away from a project he strongly believed in was particularly difficult.

"To the staff and the players, I want to say thank you so much for the last two years," he said. "You made me feel really happy sharing an amazing project. It's difficult now for me to finish. We were very excited to share a project which we really believed in. It makes the decision harder."

Pochettino admitted that leaving the United States was an emotional decision, but explained that his professional ambitions also played a part in accepting the opportunity at Old Trafford. "It's difficult to talk now because I'm a very emotional guy. In some parts it's a very sad decision; in another part we are professional, and we are trying to make our dreams come true," he said.

The Argentine revealed that discussions over the Manchester United move developed quickly, with the possibility first emerging shortly after his arrival in the United States last Friday. He said he informed the players once an agreement had been reached. "They were very supportive," Pochettino added, confirming that US Soccer and United had agreed he would remain in charge for the immediate international commitments.

Pochettino will oversee the United States' back-to-back CONCACAF Nations League matches against Haiti on Saturday and next Tuesday before taking up his new role. He also guided the Americans to the last 16 of this year's World Cup. The coach insisted he had not been planning a return to England's top flight when he extended his contract in August, but admitted United's approach was too tempting to reject. "I never said I wanted to go back in the Premier League," he said.

"Not too many opportunities can happen in your career with a side like Manchester United. That is difficult to turn down when it arrives. But I want to make clear that when we decided to extend, it was a commitment for the federation."

Dates and times for CAF Champions League semi-finals confirmed