SAN FRANCISCO - US e-commerce giant Amazon said Thursday that it has signed a merger agreement to acquire online pharmacy PillPack Inc to expand into the lucrative healthcare business.

Amazon did not disclose specific terms of the deal, but the acquisition will make the US online retailer to deliver pre-sorted medications to customers across the United States.

"PillPack's visionary team has a combination of deep pharmacy experience and a focus on technology," said Jeff Wilke, Amazon chief of Worldwide Consumer.

Amazon hailed PillPack as a pharmacy that provides the best possible customer experience in the United States for people who take multiple daily prescriptions.

"PillPack is meaningfully improving its customers' lives, and we want to help them continue making it easy for people to save time, simplify their lives, and feel healthier," Wilke said.

Market sources said Amazon bought the five-year-old PillPack for less than $1 billion. The online pharmacy startup was last valued at $361 million after a round of funding in 2016.

"Together with Amazon, we are eager to continue working with partners across the healthcare industry to help people throughout the US who can benefit from a better pharmacy experience," said TJ Parker, co-founder and CEO of PillPack.

The transaction, which is subject to regulatory approvals, is expected to close during the second half of 2018.