More than a third of the world's population is online while mobile phone uptake increased by more than 600 million in 2011 to around six billion, a UN agency said Thursday.

But the International Telecommunications Union (ITU) highlighted huge disparities in the cost of services, with the poorer parts of the world tending to pay the most.

"On the back of the increase in broadband services worldwide, the number of people using the Internet grew by 11 percent over the past year ... ie, 2.3 billion people," the ITU said in its 2012 report on information and communication technologies (ICT).

In terms of affordability, Macau, Norway and Singapore topped the list of 161 countries featured in the report.

Madagascar came bottom, just behind Togo and Niger.

In Africa, Internet connectivity prices were almost seven times higher than in the Americas, and 20 times higher than Europe in 2011.

Mobile phones with broadband showed the sharpest growth of all ICT sectors between 2010 and 2011, the agency said, with almost 1.1 billion subscriptions by the end of 2011.

Despite a surge in mobile phone broadband, "prices for ICT services remain very high in many low-income countries," said Brahima Sanou, director of the ITU's Telecommunication Development Bureau.

Income from the telecommunication sector reached $1.5 trillion (1.2 trillion euros) in 2010, around 2.4 percent of the world's gross domestic product, the report said.