The Colombians were “collecting material” in the Donbas for their movement “¡Aguanta Ucrania!” — “Hang On Ukraine!” — which seeks to garner support for Ukraine in Latin America. Most Latin American countries, which have traditionally been close to the United States but have been recently courted by Russia, have been reluctant to take a firm stance on the war in Ukraine.

“Russia has attacked three defenseless Colombian civilians,” Gustavo Petro, the president of Colombia, wrote on Twitter on Wednesday afternoon. “It thus violates the protocols of war.” He called on his country’s foreign ministry to “deliver a diplomatic note of protest.”

Mr. Jaramillo, a longtime politician, served as Colombia’s high commissioner for peace from 2012 to 2016 and played a leading role in the landmark 2016 peace accords between the Colombian government and the Revolutionary Armed Forces of Colombia, or FARC, the country’s largest guerrilla group. Mr. Abad’s memoir, “Oblivion,” was turned into a film by an Oscar-winning director, Fernando Trueba, last year.

“All our thoughts are with Victoria,” Mr. Jaramillo and Mr. Abad said in their statement. “Attacking civilian sites is a barbaric act.”

The missile hit the packed restaurant shortly after 7 p.m. local time, Ms. Gómez said in a televised report for France 24 outside of the destroyed building.

“What we are seeing right now are scenes of terror,” she said. “We are, in a way, alive by a miracle.”

The Colombians and some of their associates had traveled to eastern Ukraine from Kyiv on Monday to collect testimonies from soldiers and the head of a hospital as part of their campaign, according to the Spanish newspaper El País.

“Today, for me, this campaign is beginning to have a different meaning because what was a theory for us is now a reality,” said Esteban Martucci, an Argentine member of the group, in a video posted to social media.