Brasilia, Brazil's defence ministry has started installing a secure digital communication network for federal government offices, a government source said.

The system aims to protect official emails from the type of surveillance US intelligence agencies were reported last year to have carried out on Brazil's President Dilma Rousseff and her top aides, reported Xinhua.

The coordinator of the federal government's data processing service Serpro, Marcos Mello, said the system uses passwords and digital markers to safeguard emails from snooping, as well as certifying the authenticity of the email's origin.

The system employs "digital signatures and encryption to ensure the integrity and confidentiality of the message".

"All the security tests were done" on the system, including "a simulated break in", Mello added.

Government intelligence worked on developing the software with the help of the Federal University of Santa Catarina.

The system is expected to be fully installed at the defence ministry by June 30, and in all federal government offices by the end of 2014.

Last year, documents leaked by US intelligence worker-turned-whistleblower Edward Snowden showed the Washington-based National Security Agency (NSA) monitored the email accounts of Rousseff, several members of her cabinet, and the state oil giant Petrobras.

Brazil accused Washington of corporate spying and Rousseff instructed Serpro to develop a secure email network for government use. She also denounced the spying at the United Nations and called for global internet governance to protect individual privacy.