Brazilian President Dilma Rousseff postponed a long-planned state visit to the United States on Tuesday, the most serious diplomatic fallout yet from Edward Snowden's leak of Washington's spying secrets.

While both sides couched the cancellation in diplomatic terms, it marks an embarrassment for US President Barack Obama and a blow to his efforts to improve ties with the key Latin American power.

The visit had been scheduled for Oct 23 in Washington, but was called into question after documents leaked by Snowden, a former National Security Agency contractor, revealed the extent of US spying on its Brazilian ally.

Obama has been trying to defuse the dispute during talks with Rousseff on the sidelines of this month's G20 summit, and he spoke to her again on Monday by telephone.

But Brazil was unmoved, and on Tuesday Rousseff brought an end to the speculation, confirming that her trip was off.

"The two presidents decided to postpone the state visit since the outcome of this visit should not be conditioned on an issue which, for Brazil, has not been satisfactorily resolved," Rousseff's office said.

Her statement reflected Brazil's anger over Snowden's disclosures that the NSA spied on her e-mail communications and on the state-run energy giant Petrobras.

"The illegal interceptions of communications and data of citizens, companies and members of the Brazilian government represents a serious act which violates national sovereignty and is incompatible with democratic coexistence between friendly countries," Rousseff's statement said.

David Fleischer, a Brasilia-based international expert, described the visit's postponement as a diplomatic "slap in Obama's face". He linked the move to Rousseff's slumping popularity since last June's nationwide street protests, ahead of next year's presidential polls.

"She is showing firmness toward Obama, the world's most powerful leader, and this goes down well with the Brazilian public," Tullo Vigevani, a Sao Paulo University analyst, said.

In Washington, White House spokesman Jay Carney said, "It's because the relationship is so important and because it has so many facets that the president agrees with this decision they made together to postpone the visit."

Insisting that another, later visit could be organized, Carney added, "It should not be overshadowed by a bilateral issue, no matter how important or challenging the issue may be."

The spying row stems from allegations made by Snowden, who fled the United States and revealed the scope of the NSA's activities to Brazil-based journalist Glenn Greenwald.

In July, the Brazilian daily Globo — citing documents provided by Snowden, who has been granted temporary asylum in Russia — reported that US agencies eavesdrop on Brazilians' phone calls and Internet communications.

The report said Washington maintained an intelligence base in Brasilia, part of a network of 16 such stations around the world.

Brazilian Communications Minister Paulo Bernardo dismissed claims by US officials that the NSA was only collecting metadata logs of phone numbers called and the duration of such calls and not listening in on calls. Washington, he said, is conducting a "much deeper surveillance".

Agence France-Presse