WASHINGTON, April 21, 2011 (AFP) - U.S. lawmakers are seeking an explanation from Apple following claims that iPhones and iPads constantly log the location of the devices and store the information in a hidden file.

Senator Al Franken, a Democrat from Minnesota, sent a letter to Apple chief executive Steve Jobs on Wednesday, while Democratic Representative Edward Markey of Massachusetts sent Jobs a letter on Thursday.

The letters came after a pair of British security researchers, Alasdair Allan and Pete Warden, said the position-logging feature is contained in iOS 4, the operating system for the iPhone and iPad released in June.

Meanwhile, The Wall Street Journal reported that Google's Android smartphones also regularly transmit their locations back to Google.  

Google and Apple are storing location information to help them tap the $2.9 billion market for location-based services, according to the paper.

In a statement, Markey said Apple "needs to safeguard the personal location information of its users to ensure that an iPhone doesn't become an iTrack.

"Collecting, storing and disclosing a consumer's location for commercial purposes without their express permission is unacceptable and would violate current law," he said.

In his letter to Apple, Markey asked whether the researchers' report was accurate and, if so, how the company was using the information being collected.

Markey asked for a response within 15 business days.

According to Allan and Warden, iOS 4-equipped iPhones and iPads store latitude and longitude coordinates along with a time stamp, probably through cell-tower triangulation.

They noted that cellphone companies typically have access to this data but it is not usually stored on a mobile device itself.

The Journal cited research firm Gartner Inc., which said the location-information market is expected to rise to $8.3 billion in 2014.