President Obama: "The US will do more than strengthen its defences"
President Barack Obama has pledged his administration "will not rest" until all those behind an alleged plot to bomb a US plane are brought to justice.
In his first public comments on last Friday's incident, Mr Obama said he had ordered two reviews - of US terrorism databases and air travel screening.
The accused, Umar Farouk Abdulmutallab, a Nigerian, had a visa and was allowed to fly despite being on a watch-list.
Mr Obama spoke after it emerged a wing of al-Qaeda had claimed the plot.
The US president said only the "quick and heroic actions" of passengers and crew had averted disaster.
Call to vigilance
The 23-year-old accused, who is being held at a prison in the US state of Michigan, was restrained while allegedly trying to detonate a high-explosive device sewn in to his underwear.
Mr Abdulmutallab is charged with attempting to blow up the Northwest Airlines Airbus A330 from Amsterdam, which had nearly 300 people on board, as it made its final descent to Detroit.
He has reportedly told FBI investigators that there are others just like him in Yemen who will strike soon.
Officials are said to be concerned there may be more al-Qaeda-trained young men in the country planning to bring down US planes, the BBC's Imtiaz Tyab reports from Washington.
Mr Obama, speaking at a military base in Hawaii where he has been on holiday with his family, said: "We will not rest until we find all who were involved and hold them accountable."
Mr Obama said his administration had already taken steps to improve security, including extra air marshals and enhanced screening at airports.
Mr Obama said the people of America would not give in to fear, but added that its citizens should be vigilant.
He added: "Those who would slaughter innocent men, women and children must know the United States will do more than simply strengthen our defences.
"We will continue to use every element of our national power to disrupt, to dismantle and defeat the violent extremists."
US Homeland Security Secretary Janet Napolitano said on Monday airport systems had failed, and that a much-criticised earlier remark of hers that security had worked was taken out of context.
Shortly before Mr Obama spoke, al-Qaeda in the Arabian Peninsula claimed responsibility for the plot.
'War on crusaders'
In an internet statement, the group said it had co-ordinated the attack with Mr Abdulmutallab and only a "technical fault" caused it to fail.
The group also urged the killing of Western embassy workers in the region as part of an "all-out war on crusaders".
The website message said the attempted bombing was in response to US attacks against its operatives in Yemen.
Washington has stepped up military assistance to Yemen's offensive against al-Qaeda militants.
US officials said at the weekend the accused had told investigators al-Qaeda operatives in Yemen had supplied him with the bomb.
The Yemeni government has confirmed that Mr Abdulmutallab lived in the country between August and December, after obtaining a visa to study Arabic there.
Officials said that there was "nothing suspicious about his intentions" to visit the country.
But his father, a top Nigerian banker, voiced fears to the US embassy in Abuja weeks ago that his son was becoming radicalised.
But officials did not revoke his two-year multiple-entry visa, which was issued in June 2008.
Mr Abdulmutallab's name was added to the Terrorist Identities Datamart Environment database, but not put on a no-fly list.