Amazon Prime is a subscription service offering free delivery and access to Amazon's TV shows. Members in the US currently receive free two-day delivery, but the plan is to cut that to one day.

Prime customers already get free one-day delivery in some parts of the UK. Amazon plans to spend $800m (£620m) to cut delivery times elsewhere.

It did not say when delivery times would be cut but said it expects to make "steady progress" this year.

Walmart and Target have been improving their delivery times in the US and offer two-day shipping on many items.

Amazon's move is an effort to stay ahead of those rivals.

It already ships many items to US cities within a day, but analysts say extended that service to more remote parts of the country will be difficult.

"Amazon is cranking it up a notch, trying to set themselves apart," said Cathy Morrow Roberson, a former UPS analyst who founded consulting firm Logistics Trends & Insights.

"I don't know how they are going to do it in Little Town USA," she said.

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