Colombia has confirmed that an Ecuadorean was killed when its troops attacked a rebel camp inside the neighbouring state three weeks ago.
Ecuador broke off diplomatic ties with Bogota after the attack
Defence Minister Juan Manuel Santos said his body was taken to Colombia after the raid along with that of top leftist Colombian rebel Raul Reyes.
Ecuador's president earlier warned of diplomatic tension if an Ecuadorean was proven to have died in the attack.
There was no immediate reaction from Rafael Correa's office.
He had said that Ecuador would not forgive the killing of Franklin Aisalia, whose family reported his death in the raid.
Colombian planes bombed the Revolutionary Armed Forced of Colombia (Farc) camp on 1 March, killing more than 20 people.
Mr Correa broke off diplomatic relations with Bogota after the attack.
News that Bogota has confirmed killing an Ecuadorean threatens to plunge the two countries back into diplomatic crisis, and perhaps again put the entire Andean region on a war footing, the BBC's Jeremy McDermott reports from Colombia.
Confirming that an Ecuadorean citizen had been killed, Colombia's defence ministry said the dead man appeared to have been a member of the Farc who specialised in helping rebels cross into Ecuador to hide.
Aerial photos show the ruins of the Farc camp inside Ecuador
Defence Minister Santos identified the dead man only by his alias, Lucho.
It was not immediately clear if this was, in fact, Franklin Aisalia.
Mr Aisalia's family say they have identified his body from news photos.
Ecuador's president promised to "start an extremely strong diplomatic fight" if the death of one of his citizens was confirmed.
Mr Santos said he hoped the Ecuadorean authorities would "not let themselves be taken advantage of by criminals".