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Jamaal Charles has signed a contract extension with the Kansas City Chiefs. ((Getty Images))

The Kansas City Chiefs have signed running back Jamaal Charles to a five-year contract extension, continuing their plan to lock up their core of young players.

Charles confirmed the signing on his Twitter account, but the team refused to comment on the contract or even say if Charles had signed an extension.

The deal is worth a reported $13 million US in guaranteed money for Charles, who went into Sunday's game at San Diego leading the Chiefs in rushing. His 1,137 yards were third in the NFL and he had the highest per-carry average at 6.2 yards.

Earlier this year, linebacker Derrick Johnson signed a contract extension that could be worth as much as $34 million. Charles and Thomas Jones have made the Chiefs the No. 1 running team in the NFL, averaging more than 175 yards per game after 12 games.