PARIS  Youth unemployment across the world has climbed to a new high and is likely to climb further this year, a United Nations agency said Thursday, while warning of a “lost generation” as more young people give up the search for work.

The agency, the International Labor Organization, said in a report that of some 620 million young people ages 15 to 24 in the work force, about 81 million were unemployed at the end of 2009  the highest level in two decades of record-keeping by the organization, which is based in Geneva.

The youth unemployment rate increased to 13 percent in 2009 from 11.9 percent in the last assessment in 2007.

“There’s never been an increase of this magnitude  both in terms of the rate and the level  since we’ve been tracking the data,” said Steven Kapsos, an economist with the organization. The agency forecast that the global youth unemployment rate would continue to increase through 2010, to 13.1 percent, as the effects of the economic downturn continue. It should then decline to 12.7 percent in 2011.