The White House also released a report on Thursday of how the alleged bomber in the December 25 failed attack, Umar Farouk Abdulmutallab, managed to elude the authorities and board the Detroit-bound plane with explosives.
The six-page summary of the report given to Obama stated that US intelligence officials had received unspecified "discrete pieces of intelligence" as early as October to identify the 23-year-old Nigerian as an al-Qaeda operative and keep him off the plane.
But officials did not increase their focus on the threat and did not pull together fragments of data needed to foil the scheme, said the summary.
It appeared, Obama said, that the "incident was not the fault of a single individual or organisation, but rather a systemic failure across organisations and agencies".
"I am less interested in passing out blame than I am in learning from and correcting these mistakes to make us safer. For ultimately the buck stops with me," he added.
"As president I have a solemn responsibility to protect our nation and our people, and when the system fails, it is my responsibility."
'War against al-Qaeda'
Still, in a year when midterm congressional elections will be held, and amid opposition accusations that the US commander-in-chief is weak on national security, Obama struck a tough tone.
He ordered all involved agency heads to set up internal accountability units to review efforts to make changes, saying his administration "will measure progress".
And he warned: "We are at war against al-Qaeda. We will do whatever it takes to defeat them."
Abdulmutallab was overpowered by other passengers on Northwest Airlines Flight 253 after setting himself and part of the cabin on fire.
Days after the attack, al-Qaeda in the Arabian Peninsula, based in Yemen, claimed it was behind the attempt.
Yemen and Britain - Abdulmutallab spent time studying in both - have traded accusations that each nation was where he was radicalised by al-Qaeda.
Abdulmutallab was indicted by a US jury in Michigan on Wednesday on six counts, including the attempted murder of the other 289 passengers and crew on board and attempting to use a weapon of mass destruction.
He is expected to appear in a Detroit court on Friday - his first public appearance since his arrest.
"We are at war against al-Qaeda. We will do whatever it takes to defeat them"
Meanwhile, Janet Napolitano, Obama's secretary for homeland security, said on Thursday that she would travel to Spain this month to meet her foreign counterparts to seek tougher international aviation security measures.
She also told reporters that the US was scheduled to deploy 300 additional advanced imaging scanners at US airports this year and may deploy even more machines.
US authorities have already imposed stricter screening regulations for US-bound airline passengers from Yemen, Nigeria and 12 other countries, including possible full-body pat-downs, searches of carry-on bags, and full-body scanning.
But some analysts have questioned the efficacy and rational of the so-called enhanced screening rules, complaining of delays and discrimination.