BOGOTA (AFP) -- Colombia's defense minister resigned late Sunday, becoming the second cabinet minister to leave the government of President Alvaro Uribe in 72 hours, a government spokesman announced.

As the civilian head of the country's military and police, Martha Lucia Ramirez was the main architect in the war against the country's two leftist guerrilla movements and its right-wing paramilitaries.

Uribe has taken a tough line against illegal armed groups since he took office in August 2002, and planned a sweeping reorganization of Colombia's military and police.

Ramirez, 49, was an Uribe confidant, a former trade minister and a former ambassador to France. She was replaced by Jorge Alberto Uribe Echavarria, a 63-year-old insurance businessman.

Her resignation follows the resignation Thursday of Interior and Justice Minister Fernando Londono, who was rebuked by Uribe for telling Congress that the president would leave office and call early elections if reforms he proposed were not approved.

Both Ramirez and Londono were considered close political allies of the popular president.

Despite soaring approval ratings, Uribe supporters lost ground in an October 25 vote, when a leftist was elected mayor of Bogota -- one of the most important elected positions in the country -- and several Uribe-backed reform proposals were defeated in a referendum.

Since the vote legislators have increased their opposition to the president.

The brief statement announcing the resignation said nothing about why Ramirez -- the first female defense minister in Colombian history -- resigned, but tension had been rising in past days between her and the top military brass.

Ramirez recently criticized the head of the national police, Teodoro Campo, during a congressional hearing for not informing her about the details of a drug bust.

She had also clashed with the outspoken commander of the armed forces, Army General Jorge Enrique Mora, as well as the former head of the air force.

A top military official who asked not to be named told AFP late Sunday that the military brass was unhappy with her, but became especially angry after she hired two consultants -- a Spaniard and an American -- to restructure the defense ministry.

The military officers were unhappy with foreigners meddling in their affairs, but also angry that their opinion was being ignored, the official said.