Nations must unite to tackle international terrorism: Obama

US president Barack Obama on Saturday asked countries around the world to come together to meet the common global challenge of terrorism which has been claiming lives of innocent people from Manhattan to Mumbai.

He also sought concerted action to address other "unprecedented problems" of climate change, nuclear proliferation and recession, saying that he believes it is important to acknowledge that no single nation can solve these global issues alone.

But, working with other nations, the US can lead the way in overcoming these challenges, Obama said in his first weekly radio and internet address on his return from a successful week-long trip to Europe.

Be it the current economic crisis, or that of terrorism which has been claiming lives of innocent people from Manhattan to Mumbai; and climate change; current global challenges do not recognise any border, he argued.

"These are challenges that no single nation, no matter how powerful, can confront alone," Obama asserted, adding that the US must lead the way.

"But our best chance to solve these unprecedented problems comes from acting in concert with other nations," he said.

Referring to the recently concluded G-20 Summit in London, Obama said he met with leaders of the G-20 nations to ensure that the world's largest economies take strong and unified action in the face of the global economic crisis.

"Together, we've taken steps to stimulate growth, restore the flow of credit, open markets and dramatically reform our financial regulatory system to prevent such crises from occurring again – steps that will lead to job creation at home," he said.

"It is only by working together that we will finally defeat 21st century security threats like al-Qaeda," Obama said.

He said it was heartening that NATO allies united in Strasbourg behind Washington's Af-Pak strategy and contributed important resources to support American effort there.

"It is only by coordinating with countries around the world that we will stop the spread of the world's most dangerous weapons," he said.

"That is why I laid out a strategy in Prague for us to work with Russia and other nations to stop the proliferation of nuclear weapons; to secure nuclear materials from terrorists; and ultimately, to free the world from the menace of a nuclear nightmare," Obama said.

Obama asserted that at this critical point of history, nations around the world cannot afford to talk past or allow old differences to prevent them from making progress in areas of common concern.

"Instead, we have to find – and build on – our mutual interests. For it is only when people come together, and seek common ground, that some of that mistrust can begin to fade. And that is where progress begins," he said.

"Make no mistake: we live in a dangerous world, and we must be strong and vigilant in the face of these threats. But let us not allow whatever differences we have with other nations to stop us from coming together around those solutions that are essential to our survival and success," Obama said.