BOGOTÁ, Colombia (AP) — Authorities in Colombia doubled down Monday on their claim that guerrilla troops are operating in Venezuela with the support of President Nicolás Maduro a week after similar allegations presented at the United Nations were marred by erroneous photographs.

Colombia's Ministry of Defense released new images showing now-captured or deceased rebels posing for photographs in front of Venezuelan monuments. The presentation also contains purported letters from Colombian rebels talking about their activities inside the neighboring Andean nation.

Colombian President Iván Duque came under fire last week after making a presentation at the U.N. General Assembly in which he blasted Maduro for harboring National Liberation Army rebels, offering a 128-page dossier with photos as proof.

At least one of the photos alleging to show rebel activity in Venezuela was shot in Colombia. The government has refused to release the dossier. But the embarrassing episode has already led to the firing of Colombia's chief military intelligence officer.

Gen. Oswaldo Pena in a Letter to Duque said he was retiring for personal reasons but acknowledged that "as a general of the republic, I am conscious of the need to take responsibility for my actions and those of my subalterns, so am acting accordingly."

Colombia's ELN and FARC rebels have long sought refuge beyond that country's borders — in Brazil, Ecuador and Venezuela — although usually for short periods of time and, until now, with no known logistical support of those countries' governments except when Duque's predecessor was engaged in peace talks with the rebel groups.

Maduro has also insisted that Colombia is sheltering right-wing militias aimed at seeking his overthrow. But the coordinates of two of the three alleged "terrorist" camps that his Vice President Delcy Rodriguez presented in a speech at the U.N. General Assembly correspond to locations in the middle of the Caribbean sea.

While the two leaders trade barbs, Maduro on Monday showed a greater willingness to resume negotiations with opposition leader Juan Guaidó.

"If it was up to us, we'd have done it already," Maduro said at press conference about the prospect of returning to talks sponsored by Norway that he abruptly broke off last month over what he said was the opposition's support for stiff new U.S. sanctions.

He said that for talks to resume, the U.S. must lift the sanctions and cease all of its "military threats" against his socialist government.