Pegasus software infects iPhones and Android devices to enable operators to extract messages, photos and emails, record calls and secretly activate microphones and cameras.
Mr Petro revealed the news in a televised address to the nation, saying that he had learned of the purchase through a confidential document.
The president said that Colombia’s police intelligence directorate (Dipol) had made two payments of $5.5m (£4.2m) each to Israeli surveillance firm NSO, which had developed the spyware.
NSO has said in the past that its software is intended for use against criminals and terrorists and is made available only to military, law enforcement and intelligence agencies from countries with good human rights records.
But Mr Petro queried how $11m in cash could have left the country without any trace of it being recorded in the published budget – and why.
“It is a laundering of assets made from our own state to disrupt the communications of whom?” he asked.
Pegasus spyware hit the headlines in 2021 when a list of 50,000 phone numbers of suspected victims of hacking was leaked to major media outlets.
Among those believed to have been targeted were activists, journalists and politicians from around the world.
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