Former guerilla fighter Gustavo Petro on Sunday took oath as Colombia’s president, and pledged to unite the country against inequality and climate change, Reuters reported.

Petro, a former member of the rebel group M-19, is the South American country’s first leftist president.

He was sworn in by Senate President Roy Barreras at the Bolivar Plaza in the capital city of Bogota. About one lakh citizens, including Spain’s King Felipe VI, attended the oath-taking ceremony.

Petro said that his government will form policies to end long-standing inequalities, and promised to ensure solidarity with the country’s most vulnerable citizens, the Associated Press reported.

The newly-elected president said he is willing to start peace talks with rebel groups and added that his government may give members of armed groups reduced sentences if they provide information about drug trafficking.

“We call on all those who are armed to leave their arms in the haze of the past,” he said. “To accept legal benefits in exchange for peace, in exchange for the definitive non-repetition of violence.”

Petro also urged the United States to change drug policies that focused on the prohibition of substances like cocaine.

“It’s time for a new international convention that accepts that the war on drugs has failed,” he said. “Of course peace is possible. But it depends on current drug policies being substituted with strong measures that prevent consumption in developed societies.”

The 62-year-old said that climate change had to be fought globally, but this had to be done especially by countries that emit the highest volumes of greenhouse gases.

Petro also promised free public university education and announced that his government would bring changes in the health care sector. He added that fighting hunger would be a top priority for him.