Online retail colossus Amazon.com Inc. delivered more than 2 billion items for third-party sellers worldwide in 2016 through its Fulfillment by Amazon (FBA) service, the company said Wednesday.

Under its FBA program, Amazon opens its fulfillment network to outside sellers. The Seattle-based company acts like a third-party logistics firm (3PL), storing clients' products in Amazon fulfillment centers for a fee, then picking, packing, shipping, and providing customer service for the items.

The volume of products flowing through that FBA network has been growing fast, and in 2016 the total grew with a last-minute surge as FBA items shipped worldwide rose more than 50 percent year over year during the holiday season, including more than 28 million items ordered from sellers on Cyber Monday alone, according to Seattle-based Amazon.

Another major growth factor was international sales, as FBA units shipped grew more than 80 percent for sales outside the U.S., including Amazon sellers from more than 130 countries fulfilling orders to customers in 185 countries, the company said.

"2016 was a record-breaking year in sales worldwide for sellers on Amazon," Peter Faricy, VP for Amazon Marketplace, said in a release. "The Amazon Marketplace empowers brand owners and retailers of all sizes, many of them small businesses, to reach customers around the world... . Sellers are choosing Amazon because we help them build and grow their businesses with impactful programs like Seller Fulfilled Prime."

The firm's "seller-fulfilled prime" program allows sellers to use their own warehouses to fulfill Amazon e-commerce orders within a two-day delivery window, instead of shipping them to an Amazon-owned DC first. The option is available to members of Amazon Prime, the paid subscription service that grants customers two-day shipping on certain products for no additional charge.