?U.S. President Barack Obama has called the one-day London Summit "very productive" and "historic," saying it was the first major step in tackling the world economic challenges.

"By any measure the London Summit was historic," he told a news conference following discussions with other G20 leaders, "not only because of the size and scope of the challenges we face, but also because of the timeliness and magnitude of our response."

"The challenge is clear, and the global economy is retracting," he said, noting the world is now at the "turning point of our economic and global recovery."

"Today the world's leaders have responded with a set of unprecedented and coordinated actions," Obama said. The strong consensus in rejecting protectionism and the agreements reached at the summit signaled support for open markets, he added.

"History tells us that turning inward can help turn a downturn into a depression," Obama said. "Today we have learnt the lessons of history and we are committed to growth and job creation."

"In an age where our economies are more closely linked than ever before, the whole world is touched by this devastating downturn," the president said.

He said there had been agreements on facilitating "bold action to help developing countries" and injecting huge sums into the International Monetary Fund (IMF) to help struggling economies.

He also pledged to help those most vulnerable in the world, saying he would seek authority from the U.S. Congress to enable 448 million dollars to be diverted to help African and Latin American nations.

These "future markets" would one day drive economic growth, Obama said.

On the implementation of a better regulatory system, Obama stressed the need to "put an end to bust and bubble economic policies," and highlighted his agreements with the G20 partners on greater transparency and new regulations on hedge funds and tax havens.

The president acknowledged that it's not easy to make a deal and not everything was solved since "each country has its own non-negotiable issues," and more work needs to be done.

"This (summit) is not a panacea but it is a critical step," he said, "but we may have to take additional steps until we get it right."

Obama admitted that his country "may not always have the best answer" to the problems the world faces.

"Ultimately the challenges of the 21st century cannot be met without collective action. Agreement will almost never be easy, and result will not always come easy. But I am committed to respecting different points of view and to forging a consensus instead of dictating our terms. That's how we made progress in the last few days and that's how we will advance the deals in the months and years to come," Obama said.

"In a world that's more and more interconnected we all have responsibilities to work together to solve common challenges. And although it will take time, I am confident that we will rebuild global prosperity if we act with a common sense of purpose, persistence and the optimism that the moment demands," he added.

(Xinhua News Agency April 3, 2009)