MEXICO CITY (Reuters) - A group of human and digital rights activists said on Tuesday that the Mexican government had failed to properly investigate allegations their smartphones were infected with spying software. They have asked for an independent investigation.

Mexico's President Enrique Pena Nieto attends an event with the Mayor of Asuncion Mario Ferreiro (not pictured), in Asuncion, Paraguay January 18, 2018. REUTERS/Mario Valdez

Activists, human-rights lawyers and journalists filed a complaint in June with the attorney general’s office, claiming the government had infected their phones to spy on them with software known as Pegasus, which Israeli company NSO Group allegedly sold to Mexico’s government.

“Since filing the complaint we said we did not trust the attorney general’s office would be able to investigate itself, since there is evidence it was that agency that purchased the malware,” the activist groups said in a joint statement.

The group includes the Miguel Agustin Pro Juarez Human Rights Center (Prodh), human rights advocacy group Article 19, Mexicans Against Corruption and Impunity and digital rights group R3D.

Mexican President Enrique Pena Nieto has asked the attorney general’s office to investigate the charges the government spied on private citizens, saying he wanted to get to the bottom of the accusations he called “false.”

“President (Pena Nieto) condemned the investigation to failure, threatening the accusers and concluding prematurely the charges were false,” said the statement.

Citizen Lab, a group of researchers based at the University of Toronto’s Munk School of Global Affairs, has said it found a trace of the Pegasus software in a phone belonging to a group of experts backed by the Inter-American Commission on Human Rights who investigated the 2014 disappearance of 43 students.

U.N. human rights experts called on the government of Mexico in July to “cease the surveillance immediately” of activists and journalists and to conduct a fully impartial investigation into the illegal spying.

The group of activists said Mexican authorities have not followed up on several leads, even failing to identify and question the government officials trained to use Pegasus.

They called on candidates for July’s presidential election to make a public announcement on the need to create a panel of independent experts to investigate the case.

Left-wing candidate Andres Manuel Lopez Obrador is leading in polls for the July vote. He is followed by Ricardo Anaya of the left-right coalition “For Mexico in Front” and trailing in third is Jose Antonio Meade of Pena Nieto’s ruling Institutional Revolutionary Party (PRI).