Colombian police announced on Sunday they had intercepted and killed two FARC dissidents who had rejected the historic 2016 peace deal Londono had signed with the government.
Londono, also known as Timochenko -- now leader of the political party formed by the ex-rebel movement -- told reporters the plot had compromised his movements in Bogota and around the country.
"I was informed that an attack plan had been discovered and that the unit which was to carry it out was already trained -- that they had decided not to do it in Bogota because it was deemed too complicated, and wait until I moved to the provinces."
Police said they had shot dead two men in a gunbattle, identifying them as FARC dissidents.
Londono said hearing of the deaths was "painful, because it was two guys, two ex-guerrillas who were convinced to come and kill a traitor."
The two were members of a dissident group led by Hernan Dario Saldarriaga, also known as "El Paisa", police said.
He was one of three members of the FARC leadership -- including the organization's number two and chief negotiator, Ivan Marquez -- who announced a return to arms last August.
News of the assassination bid sparked renewed calls on the government by the UN's mission in Colombia for more protection for former rebels
"Peace cannot be fully achieved if the courageous voices of social leaders continue to be silenced by violence, and if ex-combatants who have given up their weapons and are committed to reintegration continue to be killed," mission chief Carlos Ruiz told a meeting of the UN Security Council on Monday.
Last year was the deadliest for ex-FARC combatants in Colombia since the 2016 peace agreeement.
The total of 77 deaths in 2019 surpassed the 65 murders recorded in 2018 and the 31 in 2017, the UN said.
FARC, the Revolutionary Armed Forces of Colombia, transformed itself into a political party after some 7,000 former combatants disarmed as part of the peace agreement.