He also said that the legal rationales used to approve the use of torture were a "mistake".
Break with Bush
Al Jazeera's Rob Reynolds said Obama's answers on torture left little doubt as to his personal position on the issue.
However, the US president has also made it clear he considers it up to the justice department to decide on any prosecutions of those who drafted the legal opinions authorising the methods.
Obama has played down any ideas of such prosecutions, although he has said he could be open to a bipartisan congressional investigation.
The president covered a wide range of topics in the news conference to mark his first 100 days in office, which have seen a firm break with the administration of his predecessor, George Bush, on issues ranging from war and recession to healthcare, climate change and the use of torture to interrogate suspects.
He has signed a law to close the US prison facility at Guantanamo Bay in Cuba, banned the use of torture on so-called terror suspects, steered a $787bn economic stimulus package through congress and pledged to withdraw most US troops from Iraq by August 2010.
Questioned on Iraq, he said the recent "spectacular" bombings there were a cause for concern but that civilian deaths were lower than in the past, adding that the US was still pressing the Iraqi government to make progress.
On Pakistan, Obama said Washington had "huge strategic interests" in the country and said that while he was confident the country's nuclear arsenal was safe, he remained very concerned about the nation's stability.
On the global swine flu crisis, Obama said the US continued to "closely monitor" the situation and reassured US citizens the government was taking all steps necessary.
Describing his first 100 days as a "good start", he nonetheless warned that the US faced further economic challenges on the domestic front as the US recession continues to bite despite Congress passing his $3.4 trillion budget on Wednesday.
"I am proud of what we have achieved, but I am not content. I am pleased with our progress, but I am not satisfied," he said at a news conference in Washington DC on Wednesday.
|Obama said he still had to clear the
"wreckage' of the US recession [EPA]
"[This is why] you can expect an unrelenting, unyielding effort from this administration to strengthen our prosperity and our security – in the second hundred days, and the third hundred days, and all the days after."
Obama listed the steps his administration had taken over the past 100 days, pointing to the passing of the revised draft budget by congress, the expansion of healthcare and tax cuts for working class families and a housing plan to aid homeowners.
But he said his administration still had to "clear away the wreckage" of the US recession and warned that with millions of Americans still without jobs the US "cannot go back to an economy that is built on a pile of sand".
His comments came the same day that the US commerce department said the country's economy shrunk by 6.1 per cent in the first quarter of 2009 amid cuts by businesses and a drop in exports.
The tradition of marking the first 100 days of US presidencies dates back to Franklin D Roosevelt in the 1930s, who used the first 100 days of his presidency to put in place the main components of his programmes aimed at pulling the US out of the Great Depression.