Cisco Systems Inc. Chairman and CEO John Chambers delivers a keynote address in Las Vegas, Nevada, on January 7, 2014

Cisco chief executive John Chambers has complained to US President Barack Obama about the National Security Agency's spying practices, saying they were harming overseas business for US tech firms.

"This issue affects an entire industry," the head of the telecom equipment maker said in a letter dated Friday obtained by AFP.

Chambers referred in particular to recent media reports that the NSA had intercepted and modified IT and telecom equipment on its way from manufacturers to customers.

One of the manufacturers was Cisco, which is a top supplier of networking equipment.

"If these allegations are true, these actions will undermine confidence in our industry and in the ability of technology companies to deliver products globally," Chambers warned.

"We simply cannot operate this way.

"We understand the real and significant threats that exist in this world, but we must also respect the industry's relationship of trust with our customers."

Chambers urged Obama to create new rules of conduct "to ensure that appropriate safeguards and limits exist that serve national security objectives, while at the same time meet the needs of global commerce."

Without such rules, "we are concerned that our country's global technological leadership will be impaired," Chambers said.

A Cisco spokesman confirmed that Chambers had written to Obama but declined to comment on the content of the letter.

Mark Chandler, Cisco senior vice president in charge of legal issues, had said earlier in the week on the company's blog that some actions by the US government had "overreached."

"We comply with US laws, like those of many other countries, which limit exports to certain customers and destinations," Chandler said.

"We ought to be able to count on the government to then not interfere with the lawful delivery of our products."

Several players in the US tech sector have already registered complaints following revelations of the NSA's vast online surveillance program.

Facebook founder Mark Zuckerberg has said he spoke to Obama by telephone in mid-March to express "frustration over the damage the government is creating for all of our future."

Explore further Obama meets Internet bosses on surveillance (Update)

© 2014 AFP