The actor said the United States should consider "going to Colombia and doing whatever it takes to end the cocaine trade."
In a harshly worded letter made public, Andres Pastrana told the actor that the source of the lucrative cocaine trade was an "enormous appetite for drugs, in particular in the United States and Europe."
Pastrana, who as president in 2000 launched an anti-drug effort with billions in aid from the United States, added that no country has sacrificed more than his own to rein in drug trafficking.
Every year, he said, thousands of innocent civilians are killed as a result of anti-drug efforts.
Inviting Willis to visit Colombia, Pastrana said "if you accept, you will see that, beyond Hollywood cliches, 44 million Colombians are waging a real war against drugs."
President Alvaro Uribe called the actor arrogant and ignorant last week, saying his comments were "a shock to Colombia's dignity."