Cisco Systems Inc's chief executive officer has written a letter to U.S. President Barack Obama urging him to curtail government surveillance after evidence circulated showing the U.S. National Security Agency had intercepted Cisco equipment, a company spokesman said on Sunday.​

In a letter dated May 15, John Chambers, chief executive officer and chairman of the networking equipment giant, warned of an erosion of confidence in the U.S. technology industry and called for new "standards of conduct" in how the NSA conducts its surveillance.

"We simply cannot operate this way, our customers trust us to be able to deliver to their doorsteps products that meet the highest standards of integrity and security," Chambers said in the letter.

The letter follows the circulation of pictures on the Internet showing NSA staff opening boxes of Cisco gear, the Financial Times reported on Sunday. "There have been allegations that the NSA has intercepted IT equipment in transit from manufacturers to customers to help monitor and gain information on surveillance targets," the paper wrote.

The allegations stem from early reporting from Guardian journalist Glenn Greenwald, who has written about a number of NSA documents that were provided by former NSA contractor Edward Snowden.

In the letter, Chambers states that "if these allegations are true, these actions will undermine confidence in our industry and in the ability of technology companies to deliver products globally."

In a separate blog post on Cisco's site dated May 13, the company's general counsel, Mark Chandler, wrote that "...we ought to be able to count on the government to ... not interfere with the lawful delivery of our products in the form in which we have manufactured them."