- NEW: Colombia's defense minister condemns the attempted bombing
- Authorities are investigating to determine who planted the explosives
- A former Colombian president was scheduled to speak in the theater
- Last week a former top Colombian official survived an assassination attempt in Bogota
(CNN) -- Police defused a bomb at a Buenos Aires theater Tuesday, a day before a former Colombian president was scheduled to speak there, a judge said.
The explosive device was set to be detonated Wednesday afternoon, when former Colombian President Alvaro Uribe was scheduled to be at the Gran Rex theater, Judge Norberto Oyarbide told reporters.
"It was a simple apparatus, but one that could have caused the death of people closest to it," Oyarbide said after investigating the theater Tuesday afternoon.
A theater employee alerted authorities after finding the device, Oyarbide said.
Authorities were investigating to determine who placed it in the theater.
Colombia's defense minister condemned the apparent attack attempt and called for an investigation.
Last week, a former top official from Uribe's administration survived an assassination attempt -- a daylight bombing in Colombia's capital.
Uribe was Colombia's president from 2002-2010, and was known for his focus on improving security and his tough stance on leftist guerrillas.
Uribe is scheduled to speak at an international entrepreneurs symposium Wednesday at the Gran Rex, one of the largest theaters in Buenos Aires.
Human rights groups are planning a demonstration nearby to protest the former Colombian president's visit.
CNN's Jose Manuel Rodriguez and journalist Fernando Ramos contributed to this report.
