Apple's iPad captured 80% of the tablet computer market in the US and Canada in April to July, a report has said.

The iPad accounted for six million of all 7.5 million tablets shipped in North America during the second quarter of 2011, according to research group Strategy Analytics.

It described Apple as a "formidable market leader".

Yet it added that Amazon - which is expected to unveil its own tablet this week - could become a big challenger.

'Strong brand'

Stategy Analytics senior analyst Alex Spektor said: "Apple remains a long way ahead of its main rivals such as Motorola, Samsung, RIM, Asus and HTC.

"A combination of cool branding, user-friendly hardware, entertaining services and savvy retail distribution has made Apple a formidable market leader."

According to reports, online retailer Amazon could announce the release of its first tablet as early as Wednesday.

"Provided the pricing, screen size and hardware design are right, Amazon can be one of the main challengers to Apple's dominance," said Neil Mawston, director at Strategy Analytics.

"Like Apple, Amazon has a strong brand, compelling content, sophisticated billing systems and widespread distribution.

"In effect, Amazon's new tablet product represents a good opportunity to place an Amazon shopping cart in the hands of American consumers, offering optimised access to purchasing digital content or physical goods from the Amazon online store."

The continuing popularity of Apple's iPad comes despite its incompatibility with Adobe Flash software, meaning that users cannot view a large number of online videos.

Rivals such as Samsung are quick to highlight in their advertising that their tablets are able to use Flash.

Apple and Samsung, which makes the Galaxy range of tablets, are also continuing a number of legal disputes over patents.

On Monday, Apple declined to comment on reports that it had cut orders for iPad parts from its suppliers because of falling sales.

The study by an Asian analyst of US bank JPMorgan Chase said several suppliers had indicated that Apple had reduced its orders by 25%.

The iPad was first released in April 2010, with the second version, the iPad 2, following in March of this year.