Brazilian President Dilma Rousseff announced Tuesday her decision to postpone an official visit to Washington D.C. scheduled for Oct. 23, following the US government's failure to adequately explain its alleged spying activity in Brazil.

"Given the closeness of the scheduled visit to Washington and the lack of investigation in the matter ... the conditions are lacking for the visit to take place on the previously agreed date, " said a statement from the presidency's press advisor.

Brazil had demanded explanations from the United States on the matter and asked for an end to the surveillance.

"The illegal practices of intercepting the communications and data of citizens, companies and members of the Brazilian government constitute a serious act against national sovereignty and individual rights, and incompatible with the democratic coexistence of friendly countries," the statement said.

US President Barack Obama spoke by phone with Rousseff Monday, and said he "lamented" the possible suspension of her visit, according to sources at the presidential palace.

The information that the US was spying on Brazil was first brought to light by documents leaked by former National Security Agency contractor Edward Snowden and further detailed in local daily O Globo and TV program Fantastico.

The documents indicated that the US government has for years carried out a widespread surveillance scheme that monitored millions of e-mails and phone calls made by Brazilian citizens and companies, as well as foreigners in the country.

The revelations have strained the Brazil-US relations. The U. S. did not deny the surveillance, but alleged that the program was part of a strategy to prevent acts of terrorism and therefore would continue.

However, more reports later surfaced that the program even targeted the president's office and Brazil's largest state-owned oil company, Petrobras, raising more suspicions about the US government's motives and adding to tensions between the two countries.

Rousseff released an official statement condemning the spying last week and arguing that since Petrobras does not pose a threat to any government, one could only conclude that the US spying on Brazil are driven by strategic and economic motives.

Petrobras, a pioneer in deepwater oil exploration, recently discovered and mapped the largest offshore oil reserve found to date in Brazil.

Rousseff will, however, go ahead with her planned trip to New York City, where she will address the United Nations General Assembly, which began Tuesday. In the speech, Rousseff is expected to talk about the espionage problems and defend the right to privacy.