BOGOTA, July 29 (Reuters) - Nicolas Petro, son of Colombian President Gustavo Petro, has been arrested as part of an investigation into money laundering and illicit enrichment, the attorney general's office said early on Saturday.

The younger Petro, a politician in Atlantico province, had welcomed the investigation when it began in March and has previously called accusations that he took money from drug traffickers in exchange for including them in his father's peace efforts to end civil strife.

Petro said on X, the platform previously known as Twitter, that it was painful for one of his children to be jailed, but that the attorney general's office had all guarantees to proceed according to the law.

"To my son I wish luck and strength. May these occurrences forge his character and may he reflect about his own errors," the president said. "As I affirmed to the attorney general I will not intervene nor pressure his decisions, may the law freely guide the process."

Colombia's procurator said in a separate statement it will intervene in the upcoming hearings of Petro's son and his ex-wife to ensure the legal system is respected, as well as the fundamental rights and guarantees of all parties.

The president has pledged to make peace or surrender deals with rebels and crime gangs to end Colombia's 60-year internal conflict, which has killed 450,000 people.

Efforts have been met with mixed success during his first year in office. Revived negotiations with the National Liberation Army (ELN) guerrilla group have led to a ceasefire set to begin in August, while efforts to hold conversations with major crime gang the Clan del Golfo have faltered due to continued violence.