US spy agencies are not waging a vast industrial espionage campaign on behalf of American companies as alleged by intelligence leaker Edward Snowden, senior officials said.

The United States collects economic intelligence to try to assess the stability of governments and trace the financing of terror groups or dangerous weapons, according to intelligence officials, who spoke on condition of anonymity.

"The fact that we target foreign companies for intelligence is not part of any economic espionage," said one senior intelligence official.

The goal of economic intelligence efforts is "to support national security interests," and "not to try to help Boeing, " he said.

The officials' comments were part of a growing effort by the US intelligence community to argue its case after a wave of leaks by Snowden that exposed the scale of US electronic spying and sparked a global furor.

Snowden, the fugitive former intelligence contractor who has leaked a trove of classified documents, has accused the National Security Agency of waging economic espionage and scooping up commercial information regardless of its value to national security.

"If there is information, for example on Siemens, which is in the national interest, but has nothing to do with national security, they will still use this information," Snowden said in a January interview broadcast by German public television ARD.

- Industrial spying restricted -

US officials vehemently rejected Snowden's allegation and point to legal restrictions that ban industrial spying under the 1996 Economic Espionage Act.

While industrial snooping is prohibited, officials said the law provides an exemption for the intelligence community to "collect for a valid foreign intelligence purpose" such as countering the proliferaton of nuclear or other weapons, enforcing sanctions and tracking terrorist threats.

Officials said they were not aware of any US intelligence officer being prosecuted or disciplined for carrying out industrial espionage in the past.

Although US intelligence agencies were not going after trade secrets, it would be plausible and justified for the agencies to hone in on a company like Russian-owned Gazprom -- given the current crisis in Ukraine, said the official.

In such a case, the intelligence gathering would be justified based on US national security interests, whether to shape a strategic analysis of Russia or examining sanctions issues, officials suggested.

Some media coverage of Snowden's leaks had implied that the United States had spied on Brazil's state-owned Petrobas oil firm to help US oil companies but the official said "that's not true."

The officials did not confirm or discuss why Petrobas may have been a focus for the spy agencies. Documents leaked by Snowden reportedly include a slide that names the oil giant as a target, but the purpose remains unclear.

Economic intelligence gathering and analysis was an increasingly crucial element to the spy agencies' work, officials said, though it was aimed at trying to predict geopolitical trends and disrupt terrorists.

"We could care less about a bank's balance sheet," said a second official, unless the funds are linked to weapons proliferation or extremist groups.

The fact that the officials declined to be quoted by name highlighted how pervasive secrecy often hampers the intelligence community's attempts to counter Snowden and influence the public debate over electronic spying.

The top lawyer for the intelligence services acknowledged this week that the Snowden leaks had forced the agencies to reflect on how much of their work should be shrouded in secrecy.

"These leaks have forced the intelligence community to rethink our approach to transparency and secrecy," said Robert Litt, general counsel for the director of national intelligence.

Speaking at American University Washington College of Law, Litt said he disapproved of Snowden's leaks which had "seriously damaged our national security."

But if the intelligence agencies had been more forthcoming about their activities and the rules that govern them, the Snowden leaks likely would have proved less damaging, he said.

"Going forward, I believe that the intelligence community is going to need to be much more forward-leaning in what we tell the American people about what we do."