After four years of steady declines, the number of US pedestrians killed by cars rose in the first half of 2010, a study said Thursday, suggesting portable technology could be to blame.

The Governors Highway Safety Association said the 0.4 percent increase in pedestrian fatalities in the first six months of 2010 was "notable" because it followed four years where deaths had fallen by 200 on average each year.

"We are speculating at this point, but one of the reasons may be that pedestrians are using their phones, their iPods while they are walking and jogging," GHSA spokesman Jonathan Adkins told AFP.

The reversal in pedestrian safety could be the result of the recent profusion of iPods, MP3 players and other portable technology, said GHSA chairman Vernon Betkey.

"Anyone who travels in a busy city has seen countless pedestrians engrossed in conversation or listening to music while crossing a busy street," he said.

"Just as drivers need to focus on driving safely, pedestrians need to focus on walking safely - without distractions."

The number of pedestrian fatalities dropped from almost 5,000 in 2005 to less than 4,100 in 2009, official figures showed.