* Portuguese agrees three-year extension
* Forward rules out return to Manchester United (Adds quotes, details and byline)
By Iain Rogers
MADRID, Sept 15 (Reuters) - Real Madrid have moved to tie Cristiano Ronaldo to the club until the end of the 2017-18 season by agreeing a three-year contract extension with the prolific Portugal forward.
The announcement of the deal on Sunday ended speculation about a possible return to Manchester United in 2015 when his previous deal expired.
Ronaldo left the English Premier League club in 2009 to join Real for what was then a world-record fee of 94 million euros ($125 million).
Big-spending Real president Florentino Perez and the 28-year-old Ronaldo signed the new contract at the club's Bernabeu stadium and appeared before the media at a glitzy ceremony on the giant arena's VIP tribune.
Neither Ronaldo, who said 2018 could mark the end of his career, nor Perez provided details about his salary, but Spanish media reported that his net annual wage would rise to 17 million euros, making him one of the world's best-paid players.
Wearing a dark blue jacket, light shirt and blue patterned tie and with a jewelled stud glittering in each ear, Ronaldo admitted there had been interest from other clubs, including Qatar-owned Ligue 1 side Paris St Germain.
He was also asked about United and appeared to rule out a return to the city where he spent six years after joining from Sporting Lisbon in 2003.
"Everyone knows I was in Manchester for six years and it was a club that give me many, many things and I don't forget that," Ronaldo told reporters. "But Manchester, it's the past.
"Now my club in the present is Real Madrid, this is my home, my family it's here and I am really happy here.
"But I respect all the clubs, I respect the clubs who have knocked at the door to ask something about me.
"The future nobody knows but I am really happy here. I just want to win trophies for this club and I appreciate that the fans still like me a lot to be here.
"I just want to do my best on the pitch with my goals, my assists, and try to help my team mates."
Ronaldo's renewed commitment to Real is excellent news for the nine-times European champions and comes two days before they begin their latest bid for the 10th continental crown that has eluded them since 2002.
Ronaldo will likely line up alongside record signing Gareth Bale, who eclipsed the Portuguese as the most valuable player in soccer when he joined from Tottenham Hotspur for a fee of 100 million euros this month, in Tuesday's Champions League Group B opener at Galatasaray.
Wales winger Bale scored on his Real debut in Saturday's 2-2 La Liga draw at Villarreal, while Ronaldo netted his 203rd goal in his 203rd official game for the Spanish giants.
"Today is a magnificent day for Real Madrid," Perez, who has spent hundreds of millions of euros of the club's money to try to return them to the summit of world football, said on Sunday.
"Today we have realised the dream of the entire Madrid family," added the construction magnate. "Cristiano Ronaldo will be a Real Madrid player for the next five seasons."
Quizzed by a reporter about his salary, Ronaldo said being the best-paid player in soccer was not his main motivation.
"In life there are more important things than money. Yes money is important, I am not going to lie, but it was not the priority," he added.
"The priority was a project with future, to win titles. I feel integrated in this project and the money was not the problem.
"If I am first, second or third (on the list of best-paid players) that is not the most important thing. I am in very good shape."
After the contracts were signed, Perez presented Ronaldo with a silver replica of the Cibeles fountain in central Madrid, where Real traditionally celebrate titles, before they were photographed with Ronaldo's beaming agent Jorge Mendes.
($1 = 0.7542 euros) (Editing by Clare Fallon)