Thousands of protesters have gathered in Washington to demand a new American law limiting the National Security Agency's surveillance programs seen as encroaching on private life.
The protest comes amid a widening scandal revealing sweeping US surveillance on the communications of ordinary citizens and global leaders that has sparked outrage worldwide.
Exactly 12 years to the day after Congress passed the Patriot Act to expand anti-terror intelligence gathering in the wake of the September 11 attacks, the protesters called for an end to "mass spying''.
"Hey hey, ho ho, the NSA has got to go,'' chanted the protesters, estimated to number 4,500 people according to organisers on Saturday.
To cries of "stop secret government, stop US spying, stop lying'', the demonstrators brandished banners reading ``stop watching us'' under the windows of the US Capitol that houses Congress.
They handed to Congress an online petition signed by 575,000 people urging lawmakers to "reveal the full extent of the NSA's spying programs''.
The agency has been under fire by critics since fugitive leaker Edward Snowden revealed the NSA's vast snooping on Internet searches and telephone records of millions of Americans and top world leaders, including from stalwart allies France and Germany.
"It's not just Americans being caught in this dragnet. We need to stand up for the rest of the world too,'' Free Press media and technology advocacy group president and chief executive Craig Aaron told the crowd.
"It's not about right and left; it's about right and wrong.''
Trevor Timm, 28, of the digital rights group Electronic Frontier Foundation, said Saturday was the first time since the NSA crisis broke out that people had come together to defend their privacy.
"American public opinion has completely changed regarding NSA and privacy,'' said Timm, 28.
President Barack "Obama said a lot of things, now we need to see actions'', added Timm, who wore a t-shirt that read ``stop watching us.''
Nearby, another activist brandished a poster that showed a computer whose screen bore the inscription "Unplug Big Brother''.