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West Ham have completed the signing of Manuel Lanzini on a four-year contract from Al Jazira.
The 23-year-old midfielder had been on loan from UAE club Al Jazira and has now sealed a permanent switch to Upton Park.
The deal, which includes an option for a further two years, is understood to be worth around ?9million.
Jack Sullivan, the son of Hammers joint-chairman David Sullivan, confirmed the news on Twitter.
He wrote: "Lanzini is a WHU player for the next 4 seasons, with a further 2 year option."
Boss Slaven Bilic has now secured the futures of three of his key players after Dimitri Payet and Cheikhou Kouyate recently signed new long-term contracts.
Lanzini is back to full fitness following a spell on the sidelines with a thigh injury.
The Argentinian scored his sixth goal of the season with a fine 20-yard curler in the 2-2 draw at Chelsea on Saturday.
France playmaker Payet has taken most of the spotlight for West Ham this season but Sullivan senior says Lanzini is just as important.
He told the Daily Mail: "You say Payet and, yes, he is our star, but I can say Lanzini, (Michail) Antonio, (Mark) Noble, Kouyate.
"We've just given Kouyate a new deal, even though he had more than four years on his last one.
"We want to reward excellence. They have all played their part."