Walmart has thrown down the gauntlet to Amazon as it ramps up its efforts to boost online sales.

Walmart president & CEO Mike Duke told investors at Walmart’s ‘Meeting for the Investment Community 2012’ that the US giant was “playing to win” in the global e-commerce market.

“This has also been an important year of progress for us in e-commerce,” said Duke. “We’ve assembled best-in-class teams in Silicon Valley and around the world. I believe we are playing to win in a very real way now by driving innovation, working together across the entire business and investing in our vision. Our efforts are strengthening an already good business.”

Duke also revealed that Walmart’s new ‘Polaris’ search engine, which it built in-house and unveiled in August, had boosted the number of customers completing a purchase on by 15%.