President Barack Obama on Tuesday blamed a combination of human and systemic failures in security for allowing the botched Christmas Day attack aboard a U.S. airliner, in his first big test on homeland security.

Interrupting a vacation in Hawaii for the second straight day to reassure Americans that he will keep the United States safe, Obama listed several points at which red flags should have been raised to prevent a young Islamic militant from smuggling explosives onto a plane to the United States.

The reviews I have ordered will surely tell us more, but already what is apparent was that there was a mix of human and systemic failures that contributed to this potential catastrophic breach of security, Obama said.

Umar Farouk Abdulmutallab, a 23-year old Nigerian student, is suspected of trying to ignite the explosives on Northwest Flight 253 from Amsterdam as it approached Detroit on December 25.

When our government has information on a known extremist and that information is not shared and acted upon as it should have been ... a systemic failure has occurred and I consider that totally unacceptable, Obama said at a Marine Corps base near his holiday home.

The failed attack has put Obama on the defensive over domestic security, forcing communication missteps by his administration and drawing attention away from his top domestic policy priority of healthcare reform.

By going before the television cameras twice in two days, he sought to counter any impression that his vacation took precedence over a major national security issue.

We need to learn from this episode and act quickly to fix the flaws in our system because our security is at stake and lives are at stake, Obama said.

Technology may be part of the solution.

Abdulmutallab smuggled the explosives in his underpants through checkpoints in Lagos and Amsterdam and hyper-sensitive body scanners might have prevented this from happening. But the machines are expensive and also intrusive, exposing an image of the naked body on a security viewing screen.

The shares of Air Canada and WestJet Airlines Ltd, Canada's two biggest airlines, fell on Tuesday after they warned U.S.-bound travelers to expect more flight delays and cancellations as security is beefed up.

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