By Li Hongmei

US technology companies on Monday called on President Barack Obama and members of Congress to limit surveillance of citizens.

Internet giants, including Apple, Facebook and Google, also called on US leaders to set an example for countries worldwide in the wake of revelations of broad surveillance by the National Security Agency that have prompted an outcry from many US allies and civil libertarians.

"We understand that governments have a duty to protect their citizens. But this summer's revelations highlighted the urgent need to reform government surveillance practices worldwide," they wrote.

The internet firms lay out five principles for global reforms of state surveillance on a joint website.

They call for an end to mass gathering of communication data from the internet, noting governments should limit such efforts to specific suspects.

Responsible authorities and courts should be more tightly controlled, they argue. The companies, which also include Microsoft, Twitter, AOL, Yahoo and LinkedIn, also seek to be allowed to publicize how often and why governments seek user information.

The offensive follows months of revelations about surveillance by the NSA, including spying on emails and the gathering of data from internal connections between data centers at Google and Yahoo.

The companies also hope to protect their business models from a loss of trust that could damage their email, search, chat and other services. "

People won't use technology they don't trust," Microsoft general counsel and executive vice president Brad Smith said.

"Governments have put this trust at risk, and governments need to help restore it."

Obama said Thursday he would unveil "self restraints" on surveillance in coming weeks in the wake of the NSA revelations.

Obama told MSNBC that some of the revelations to the media by former government contractor Edward Snowden had raised "areas of legitimate concern," but that much of it was also "highly sensationalized."