Obama discussed the issue with presidents Dilma Rousseff of Brazil and Enrique Pena Nieto of Mexico during a working dinner at the Group of 20 summit in St. Petersburg, Russia.
"I assured President Rousseff and President Pena Nieto is that I take these allegations very seriously," Obama said Friday during a news conference. "I understand their concerns. I understand the concerns of the Mexican and Brazilian people; and that we will work with their teams to resolve what is a source of tension."
Earlier this week, Brazil's O Globo reported that the U.S. National Security Agency monitored the emails, text messages and phone calls of Rousseff as president and Pena Nieto when he was a presidential candidate. The report was based on documents leaked by former NSA contractor Edward Snowden, who was granted temporary asylum in Russia.
Brazilian lawmakers and leaders have called on Washington to give an explanation.
Because of technology's rapid changes and expanding capabilities, "it is important for us to step back and review what it is that we're doing," Obama said during the news conference. "Because just because we can get information doesn't necessarily always mean that we should. There may be costs and benefits to doing certain things, and we've got to weigh those."