Barcelona have moved to strengthen their defence by agreeing to sign the Belgium center-back Thomas Vermaelen from Arsenal on a five-year contract.

Barça did not publish any financial details on their website but the fee is understood to be in the region of £15 million.

Luis Enrique has made upgrading Barcelona's defense a big priority this summer.

Vermaelen will compete for a place with Gerard Piqué, the Frenchman Jeremy Mathieu, who joined last month from Valencia, and the Barça academy graduate Marc Bartra.

Javier Mascherano has mostly played in central defence since joining Barcelona from Liverpool in 2010 but after his performances in midfield for Argentina at the World Cup he is widely expected to feature there for the club next term.