SAN FRANCISCO — Mark Zuckerberg is defending Internet.org after several companies in India decided to pull out of the initiative amid a growing debate over free access to the Internet in the country.

Facebook’s high-profile project to bring the Internet to the developing world and get billions more online has become the target of fears it could undermine net neutrality, the idea that all online traffic should be treated equally.

Net neutrality grabbed headlines in India this week after leading mobile carrier Bharti Airtel announced a product that lets mobile app makers pay for data usage so consumers can use their apps for free.

A number of companies including travel service Cleartrip.com and media giant Times Group, owner of the Times of India, withdrew from Internet.org, expressing concern that telecom companies would get to choose which apps and services users can access and how quickly.

In a post on his Facebook page, Zuckerberg addressed the growing backlash, arguing that Internet.org’s basic free services are not a threat to net neutrality. He says Internet.org does not “block or throttle any other services or create fast lanes — and it never will.”

“Net neutrality is not in conflict with working to get more people connected,” the Facebook CEO wrote. “These two principles — universal connectivity and net neutrality — can and must coexist.”

“To give more people access to the internet, it is useful to offer some service for free. If someone can’t afford to pay for connectivity, it is always better to have some access than none at all,” he continued.

Critics were quick to pounce.

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,” India’s Save the Internet coalition wrote in the Hindustan Times.

Through Internet.org, telecommunications companies picks up the data costs so that consumers can receive basic services for free.

Zuckerberg says Internet.org is “open for all mobile operators and we’re not stopping anyone from joining.”

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. It has also launched in Indonesia on the Indosat network.

Facebook selects the apps included in Internet.org after consulting local governments and mobile operators, Zuckerberg says.

“We want as many internet providers to join so as many people as possible can be connected,” he said.

But critics say that makes it tougher for services that are not part of Internet.org to reach people with no Internet access in developing countries.

India is key to Facebook’s global ambitions. It is home to the world’s third-largest population of Internet users.

Facebook formed a partnership with Indian mobile carrier Reliance Communications to launch Internet.org in India in February.The Internet.org app offers free access to basic services such as health information and job listings.