Three percent more girls between the ages of 15 and 19 became pregnant in 2006 than in 2005, four percent more gave birth, and one percent more had abortions, the report by the Guttmacher Institute showed.
Three-quarters of a million women younger than 20, or seven percent of the 15-19 age group, became pregnant in 2006, the report said.
That made for 71.5 pregnancies for every 1,000, 15- to 19-year-old girls, compared to 69.5 pregnancies per 1,000 girls in the same age group in 2005, when the US teen pregnancy rate reached its lowest point in more than 30 years.
The rise was "deeply troubling" and "coincides with an increase in rigid abstinence-only-until-marriage programs, which received major funding boosts under the Bush administration," said Guttmacher Institute senior public policy associate Heather Boonstra.
"This just shows once again that the investment that was put into abstinence-only programs has not paid off," Boonstra told AFP.
"There's a strong body of evidence that these abstinence-only programs simply do not work: they don't help teens to either delay sex or increase contraceptive use when they do become sexually active," she said.
The rise in teen pregnancies follows a sharp decrease in the rate throughout the 1990s, which Boonstra said was largely due to better use of contraceptives by teens, and a leveling-off in the early 2000s.
A smaller proportion of the fall in teen pregnancies in the 1990s was due to less sexual activity among US teens, she said.
But in the early 2000s, contraceptive use among US teens decreased, and "certainly that is connected to this increase in teen pregnancy," said Boonstra.