Visa Inc has thrown its weight behind a mobile payments venture created by Twitter co-founder Jack Dorsey.

The credit-card company has made an unspecified investment in Square, a two-year-old service that helps businesses and consumers pay with credit cards on a mobile phone or Apple Inc iPhone, both companies said in a statement.

In return, a Visa executive gets to sit on the advisory board at Square, which is also backed by Sequoia Capital and Khosla Ventures.

Square's service employs a miniature magnetic card-reader that plugs into a device, such as an iPhone or Google Android phone. CEO Dorsey in March returned to the microblogging sensation he helped create, taking up the post of executive chairman -- in addition to his responsibilities at Square -- to oversee product development.

(Reporting by Edwin Chan. Editing by Robert MacMillan)

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