Hammers' chairman Terence Brown described the high profile double signing as the biggest deal in the club's history.

Striker Tevez and midfielder Mascherano, both aged 22, featured for Argentina at the World Cup finals and their move to Upton Park came on the final day of the transfer window.

Brown, in an interview on the London club's official website, said: "The sheer quality of the two players we have signed makes it a very exciting deal, and these are not players coming to the end of their careers - they are young players who are on their way up.

"They are also great lads - both have shown a keen interest in the club and knew all about our success last season."

Brown disclosed that the players were well aware of West Ham's history and in particular its links with England legend Bobby Moore.

"Javier even asked for the number six shirt at one point during the negotiations, as he knew it was the number that Bobby Moore had worn for us all those years ago," he reported.

The club chairman reckons the Argentine duo's arrival will help West Ham step up a gear in their bid to improve on last season's ninth place finish in the Premiership.

"We are now in a position to take the next step up as a football club, and these signings will put us in the spotlight on a worldwide scale.

"I'm sure we can all look forward to some good times ahead," said the Hammers' chief.

He added: "It is a momentous day for the football club. It is without doubt the biggest deal in our history and one that we are all very excited about."

Tevez told the club's website that he had only been told about the possibility of joining West Ham two days before the deal was completed and admitted there were other teams also interested in signing him.

He said: "I first heard about the possibility of joining West Ham 48 hours ago. I had followed the club quite a bit last season because I am a close friend of Lionel Scaloni.

"It's true, other clubs in the Premiership and around Europe were interested in signing both myself and Javier. But when we met Alan Pardew the choice was simple, he made us both feel really wanted.

"We watched every West Ham game in Argentina because of our friendship (with Scaloni) and he spoke very highly of the club, its supporters and the manager.

"I know there will be a lot of fuss around us because we are two new players from Argentina, but we see ourselves as team players, not individuals.

"That was another attraction for coming here, Mr Pardew explained that there is a great team spirit at the club, and we want to be a part of that."

The duo will report for training with West Ham for the first time on Tuesday and Mascherano added: "Mr Pardew's enthusiasm rubbed off on both of us. He talked about his vision for us and the club, and we both became very excited.

"I am also aware of some of the great players at West Ham. I know of Anton Ferdinand, he is talked about a lot in Argentina as a great player of future, while I also like Nigel Reo-Coker, who is a very dynamic captain and displays the work ethic that is clearly in place at West Ham."

The pair's move to the Premiership appears to have been smoothed by the fact that both Tezev's and Mascherano's rights are owned by Media Sports Investment, a British-based company with financial involvement in Corinthians.

MSI were linked with a takeover of the Hammers last season.

Both have been included in Argentina's squad for Sunday's friendly against Brazil at Arsenal's Emirates Stadium.