President Barack Obama today pledged "unrelenting, unyielding effort" as his administration battles with a range of challenges from recession to the threat of pandemic swine flu.

Speaking during a prime-time news conference marking his 100th day in office, the president said he was "pleased" but "not satisfied" with progress made so far.

In an optimistic note, Mr Obama said America would see "a better day", but added that it would take time and effort.

The comments came hours after Congress approved his 3.4 trillion dollar (£2.4 trillion) budget. The development means that Mr Obama's key spending plans in areas such as healthcare reform, education and green energy have been given the green light, albeit without Republican support.

After a brief update on the swine flu outbreak, Mr Obama turned to the passing of the budget.

He said: "This budget builds on the steps we've taken over the last 100 days to move this economy from recession to recovery and ultimately to prosperity."

Highlighting what he believes to be his achievements in office, the president said the near-800 billion dollar (£540bn) economic stimulus package had already saved or created more than 150,000 jobs - a fraction of the 3.5 million jobs pledged through the plan.

He also pointed towards a law that provides and protects health insurance for 11 million children and a housing plan intended to kick-start the stalled mortgage sector.

But he acknowledged that a lot more needed to be done to pull the US out of its economic crisis.

Mr Obama said: "We are off to good start. But it is just a start.

"I am proud of what we have achieved, but I am not content. I am please with our progress, but I am not satisfied.

"Millions of Americans are still without jobs and homes and more will be lost before this recession is over."

Looking at the challenges ahead, the president pointed to the threat from terrorism, nuclear proliferation and pandemic flu.

He said: "All of this means you can expect an unrelenting, unyielding effort from this administration to strengthen our prosperity and our security - in the second 100 days, and the third 100 days, and all the days after."

Despite the problems that he faces, Mr Obama appeared relaxed during the third prime-time press conference of his administration, joking with the reporters at times despite the importance of the matters being discussed.

He also ended his opening remarks on an upbeat note.

Mr Obama said: "We will rebuild a stronger nation and we will endure as a beacon for all those weary travellers beyond our shores who still dream that this is a place where all is possible."

In a Q&A session with journalists, Mr Obama was pressed on a range of topics on domestic and foreign policy.

Turning to the swine flu outbreak, the president said that now was not the time to close the border with Mexico. He likened it to shutting the stable door once the horses had bolted.

He urged vigilance in a bid to limit the disease's spread, calling on Americans to implement simple measures such as regular hand-washing and staying at home if they showed any symptoms.

In response to a question over torture, Mr Obama reiterated his opposition to interrogation techniques such as waterboarding.

Turning to the US's ailing car industry, Mr Obama said he was more optimistic that Chrysler would be saved. The car maker is facing the possibility of bankruptcy if a merger with Italian firm Fiat fails to materialise.