In a blog post, Mr Zuckerberg argued that Internet.org's basic free services were not incompatible with net neutrality - the principle that all web services should be equally accessible.

"We fully support net neutrality," he wrote. "Universal connectivity and net neutrality can and must co-exist."

But critics were quick to respond.

Writing in the Hindustan Times, India's Save The Internet coalition maintained that Internet.org is "Zuckerberg's ambitious project to confuse hundreds of millions of emerging market users into thinking that Facebook and the internet are one and the same."

Distorting competition?

At the heart of the row is Internet.org's policy of "zero-rating", whereby telecoms providers agree not to pass on the costs of handling the data traffic so that consumers can receive services for free.

Critics argue this has a distorting effect on competition, making it difficult for publishers not signed up to Internet.org to reach the hundreds of millions of poorer people in developing economies who have no internet access at all.

But Facebook disagrees, pointing out that joining Internet.org is free for web publishers and app providers.

"We're open for all mobile operators and we're not stopping anyone from joining," says Mr Zuckerberg. "We want as many internet providers to join so as many people as possible can be connected."

However, India's leading mobile operator Bharti Airtel has also been applying zero-rating to its Airtel Zero service.

This means that consumers can access certain apps for free because the app provider picks up the data bill.

Smaller developers without the resources to do the same are at a commercial disadvantage.

Better than nothing?

Facebook chooses the services offered by Internet.org after consultation with "local governments and the mobile operators" in each country, says Mr Zuckerberg.

It is this hand-picking process that appears discriminatory to many within the industry.

But Mr Zuckerberg believes that "if someone can't afford to pay for connectivity, it is always better to have some access than none at all."

In India, Internet.org has rolled out its free basic services on the Reliance network in Tamil Nadu, Maharashtra, Andhra Pradesh, Gujarat, Kerala and Telangana.

And it has also launched in Indonesia on the Indosat network.

Boycott

This week a number of firms, including travel portal Cleartrip.com and media giant Times Group, withdrew from Internet.org, claiming that the service conflicts with the principle of net neutrality.

The issue has certainly galvanised the Indian public - more than 800,000 people have sent emails to India's telecom regulator, Telecom Regulatory Authority of India, demanding a free and fair internet.

Indian telecoms companies have been putting pressure on the government to change the way so-called "over-the-top" mobile apps, such as Skype, WhatsApp, and Instagram, are licensed.

Such apps piggyback on the operators' networks and have benefited greatly from the proliferation of smartphones and the explosion in mobile content.

Operators want a bigger slice of the pie.

(BBC)