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.