The Delta variant of the coronavirus is not specifically targeting children, the World Health Organization said Friday.

The WHO's Covid-19 technical lead Maria Van Kerkhove said the evidence showed that the variant first detected in India was rather being transmitted among people who were socially mixing.

"Let me be very clear: we are not seeing the Delta variant specifically target children," the US expert told a press conference.

Delta has now been detected in 132 countries and is more transmissible than earlier versions of the virus, including other variants of concern.

The UN health agency said work was under way to gain a better understanding of the dynamics of Delta and why it is more transmissible.

"There was some suggestion that the variants were specifically targeting children, but that actually is not the case. What we are seeing is that the variants will target those who are socially mixing," Van Kerkhove said.

"What we do see is that the variants that are circulating will infect people if they are not taking the proper precautions," she said, referring to measures such as physical distancing and avoiding gathering in poorly-ventilated, crowded indoor spaces.

The WHO has published a plan detailing ways in which schools can reopen and stay open in safety.

"But we do really need to drive down transmission in the communities to make sure that they can open safely," Van Kerkhove said.