THE youngest elected president in Colombia’s history has been sworn in to office, promising to “make corrections” to a peace deal with leftist rebels.

Ivan Duque, the 42-year-old protege of a powerful right-wing former president, now faces the task of implementing the historic accord with the Revolutionary Armed Forces of Colombia (Farc) that ended a half century bloody conflict, but which remains on shaky ground.

He will also have to deal with burgeoning coca and cocaine production that has strained relations with key ally the United States and negotiate a peace with a guerrilla army.

“The moment has come for all of us to unite to fight against illegal groups,” Duque said in his inauguration speech to more than a dozen heads of state, promising to get tough on crime, drug trafficking groups and other armed and rebel factions.

The new president believes in “the demobilisation, disarmament and reinsertion of the guerrilla base” into society under the accord with the Farc. But he added that “we will make corrections to ensure that the victims receive truth, proportional justice, reparations and not a repetition” after a conflict that left at least 260,000 dead, some 60,000 missing and millions displaced.

In another nod to conservatives who have demanded tougher negotiation terms with rebel groups, Duque said he will push for a constitutional reform that makes it impossible for the government to grant amnesty to individuals who have been involved in drug trafficking and kidnappings.

Duque will have to lead peace negotiations with the National Liberation Army (ELN), a guerrilla army of some 2000 fighters that began talks with Duque’s predecessor, Juan Manuel Santos.

Last week, they kidnapped three policemen and a soldier in an attack that highlighted the government’s struggle to bring law and order to Colombia’s most remote areas.

“We have to construct a culture that respects the rule of law,” Duque said as he spoke on a large blue stage on Bogota’s largest public square.

Duque’s detractors fear he will be little more than a puppet for Alvaro Uribe, the ex-president who led a referendum defeat of the initial version of a peace accord with the Farc rebels.

Uribe is still backed by millions of Colombians, though he is perhaps equally detested by legions who decry human rights abuses during his administration.

On Tuesday, hours before the inauguration ceremony, thousands gathered in public squares in a dozen cities across Colombia to express their opposition to Duque.

At the rallies, protesters bore white flags and signs that called for the preservation of the peace deal.

Duque is taking office as a spate of attacks and the killings of social activists have underlined that peace remains a relative term. On Monday night, a motorcycle bomb exploded outside a police station in the western province of Cauca.

“If Duque is not able to solve this problem and find a way to bring the state into the countryside, we’re going to keep having the same problems we’ve had for decades,” said Jorge Gallego, a professor at Colombia’s Rosario University.

The new president has promised a harder line against drug trafficking. He intends to bring back aerial fumigation of coca crops, a policy stopped by Santos three years ago over health concerns, but is supported by the US government.

Colombian cocaine production has doubled in the past two years, according to US authorities.

Duque has undergone a rapid transformation, thanks in large part to the support of Uribe. Just four years ago, Duque was a Washington suburbanite with a job at an international development bank.

He developed close ties to Uribe there, helping the former president when he taught a course at Georgetown University.

In 2014, Uribe propelled Duque into the limelight by urging him to return to Colombia to run for office.