The US Congress Government Accountabilaity Office (GAO), called on the federal regulators on Tuesday to revise rules that measure the amount of radiation from mobile phones.
The year-long review by the office, done at the urging of lawmakers, did not suggest that cellphone use causes cancer.
But it was critical of the way the Federal Communications Commission had managed its standards, noting that the rules, which had not changed since 1996, lagged behind those of the international community, The Washington Post reported.
The FCC's regulations "may not reflect the latest evidence on the effects" of mobile phones, the GAO's report said.
What's more, when testing cellular radiation exposure on someone using an earpiece, the FCC assumed that people placed their phones at a distance, say, on a nearby table, the GAO noted. But many people kept their phones in their pockets or on their belt buckles.
The FCC "may not be identifying the maximum exposure, since some users may hold a mobile phone directly against the body while in use," the GAO said.
The office has recommended that the FCC reexamine both its exposure limits and the way it conducted their tests.
In response to the report, the FCC said that it will ask federal health agencies and others for input as it assessed its regulations.
The FCC said in June that it was contemplating whether it needed to update its rules, but the agency noted that reputable health experts had dismissed fears that cellphones are dangerous.
"The U.S. has among the most conservative standards in the world. We look forward to reviewing today's GAO report as part of that consideration," FCC spokesman Neil Grace said in a statement.
Representative Edward J. Markey (D-Mass.), who had asked the GAO to study the matter, said that the study showed that the FCC was behind the curve.
"With mobile phones in the pockets and purses of millions of Americans, we need a full understanding of the long-term impact of mobile phone use on the human body, particularly in children, whose brains and nervous systems are still developing," Markey said.
Ahead of the study's release, there had been renewed interest in the area of mobile phone radiation.
Last year, a World Health Organization report found that cellphone radiation could be carcinogenic.
A separate study from the National Institutes of Health, done in early 2011, found that 50 minutes of cellphone use altered activity in the part of the brain closest to where the phones antennas were located.
On Monday, Representative Dennis J. Kucinich (D-Ohio) introduced a bill that would put warning labels on cellphones and tap the Environmental Protection Agency - not the FCC - to lead the way in examining the effects which the radiation has on the human body.
In a statement, Kucinich said that the cellphone users have a right to know how much radiation their phones give off, particularly as people spend more time with them.
They shouldn't have to wait for the scientists to prove whether there are any harmful effects.
"It took decades for scientists to be able to say for sure that smoking caused cancer. We must allow consumers to have enough information to choose a phone with less radiation," Kucinich said.
The city of San Francisco is looking at a labeling measure that is similar to the one proposed by Kucinich.
The wireless industry's trade group, CTIA, has filed a lawsuit against the proposed ordinance.