Franco Lamolinara and Chris McManus were killed by kidnappers last week while a raid to free them was under way, according to British government sources briefed on the matter.
The case drew criticism from top Italian officials, who questioned why Rome was not consulted before the operation, which was launched by Nigerian forces with support from Britain.
Speaking in an interview with CNN on Thursday, Jonathan said: “We worked with the international intelligence system. If there was success, there would have been a collective glory. Since we did not quite succeed, well, we all take responsibility.”
“So I cannot say I will not take part of that responsibility: yes, I do. I’m the President of the country.”
Britain said it had not been possible to inform Italy of the operation until it was under way because of the fast moving situation on the ground and the “imminent and growing danger” to the hostages’ lives.
Jonathan said the raid was initiated after conversations between the captors were intercepted.
The hostages had been moved several times and there were fears they would be taken out of Nigeria, he said.
The escape of one of the alleged kidnappers during an arrest the day before the failed rescue attempt also raised fears McManus and Lamolinara would be killed, the president said.
Jonathan said he was not aware of any demand for a ransom, or of any ransom payment having been made.
“In this particular case, no family member informed security agencies that they (the captors) had reached out to them for ransom,” he told CNN.
An autopsy conducted on Lamolinara’s body on its return to Rome revealed he had been shot four times, according to Italian media reports.