Image caption OpenDoor's app helps users bypass firewalls to access restricted web sites

Chinese web users have criticised Apple after the company pulled an iPhone app which enabled users to bypass firewalls and access restricted internet sites.

The developers of the free app, OpenDoor, reportedly wrote to Apple protesting against the move.

China blocks users from accessing many websites and strictly polices internet access and censors web users.

The BBC contacted Apple for its response to the report and has yet to receive a reply.

Apple asks iPhone app developers to ensure that their apps "comply with all legal requirements in any location where they are made available to users".

It says that "developers have an obligation to understand and conform to all local laws".

But Zhou Shuguang, a prominent Chinese blogger and citizen journalist, told US-based Radio Free Asia that Apple had taken away one of the tools which internet users in China relied on to circumvent the country's great firewall.

Chinese internet users were disappointed by the move by Apple.

One said: "It was so bad that this was taken away. I can't now jump over the firewall."

Another user wrote: "Apple is determined to have a share of the huge cake which is the Chinese internet market. Without strict self-censorship, it cannot enter the Chinese market."

Many Chinese social media users have only just become aware that the app has been unavailable since July.

The developers of OpenDoor - who wish to remain anonymous - told Radio Netherlands that Apple removed the app because it "includes content that is illegal in China".

Image caption Apple says developers must conform to local laws

The station reported that the email from OpenDoor to Apple said the removal of the app was inconsistent.

"It is unclear to us how a simple browser app could include illegal contents, since it's the user's own choosing of what websites to view," the email says.

"Using the same definition, wouldn't all browser apps, including Apple's own Safari and Google's Chrome, include illegal contents?"

OpenDoor is not the first app to have been removed from Apple's App Store in China.

It has previously removed a news app by a US-based television broadcaster founded by the outlawed Falun Gong group.

Another app, which enables users to access books banned in China, was also withdrawn.

China has 591 million internet users, according to the latest official figures from China Internet Network Information Centre.

Among them, 464 million accessed the net via smart phones or other wireless devices.