Explanations provided so far by the United States concerning its alleged spying on Brazilian telephone and Internet communications are not enough, says Foreign Minister Antonio Patriota.

"Some explanations were offered, but we consider them insufficient," Patriota told reporters Monday.

Patriota said technical experts from several ministries are working to draw up a set of questions that will be submitted to the U.S. for further explanation.

"A group formed by representatives of the Justice, Defense, Science and Technology, and Foreign Ministries and the Institutional Security Cabinet will prepare a list of questions so that we can request additional clarifications," Patriota said.

Also on Monday, the Brazilian Senate invited U.S. Ambassador Thomas Shannon to a meeting on the issue, but he declined the invitation, saying he was not authorized to discuss the matter.

The Brazilian daily O Globo last week published revelations of U.S. spying on Brazil's telephone and Internet traffic, based on documents leaked by U.S. intelligence whistleblower Edward Snowden.

The O Globo reported that since 2002 the U.S. has operated an espionage base in Brasilia, Brazil's capital, through intelligence agents posing as diplomats, to spy on incoming and outgoing communications.

Brazil is among several countries that appear to be targeted on maps used by the U.S. National Security Agency for the tapping of phone and Internet data, the newspaper said.?