MEXICO CITY - The Mexican government is demanding a "clear and precise" answer from the United States for allegedly spying on President Enrique Pena Nieto, Foreign Minister Jose Antonio Meade said Tuesday.

"We want to demand an investigation and a demarcation of responsibility for alleged acts of espionage," Meade said during a hearing in the Senate, whose members have shown dissatisfaction with the government's previous response to Washington.

The response was inadequate and the case should be discussed with international organizations as it had interfered in Mexico's internal affairs, some senators argued.

The alleged espionage was leaked by former US National Security Agency contractor Edward Snowden, who said Washington had spied on Nieto before he was elected in June 2012.

Mexican authorities have already expressed disagreement with the United States in terms of security and migration issues, Meade said.

"In the dialogue with the US, we have addressed the differences in a timely and mature way that inevitably arise in a close relationship," he said.

After the disclosure of the alleged espionage, Mexico summoned the US ambassador to explain the accusation. Nieto also discussed the issue with his US counterpart, Barack Obama, during a private meeting held in Russia early September.

However, some opposition senators believed that Mexico should have a "strong" reaction and demand more explanations from the United States.