Growth in the number of people with access to the Internet is slowing, and more than half the world's population is still offline, the United Nations Broadband Commission said on Monday.
Internet access in rich economies is reaching saturation levels but 90% of people in the 48 poorest countries have none, its report said.
The access growth rate is expected to slow to 8.1% this year, down from 8.6% in 2014. Until 2012, growth rates had been in double digits for years.
"We have reached a transition point in the growth of the Internet," the report said.
The commission, set up in 2010 by the International Telecommunication Union and Unesco, the UN scientific and cultural agency, said the milestone of four billion Internet users was unlikely to be passed before 2020.
It said growth in Facebook subscribers was outpacing growth in the Internet.
"Over half the world's population - some 57%, or more than 4bn people - still do not use the Internet regularly or actively," the report said.
It blamed the cost of extending last-mile infrastructure to rural and remote customers, and a sharp slowdown in the growth of mobile cellular subscriptions globally.
By the end of this year, 3.2bn people will have some form of regular access to the Internet, up from 2.9bn in 2014. That is 43.4% of the world's population, still far short of a UN target of 60% by 2020.
Women in poorer countries were particularly disadvantaged, the report said. In the developing world, 25% fewer women than men had Internet access, a number that rises to 50% in parts of sub-Saharan Africa.
Only about 5% of the world's estimated 7,100 languages were represented on the Internet, the report said. Many Internet users could not understand Latin script, so even reading domain names was a challenge, it added.
