Baden-Baden, Germany  - NATO needs to adopt a new vision to cope with the demands of the 21st century, US President Barack Obama said during a visit to Germany on Friday.

"I don't come bearing grand designs," he said ahead of summit marking the alliance's 60th anniversary. "I'm here to listen, to share ideas, and jointly - as one of many NATO allies - to help shape our vision for the future."

Obama was speaking at a joint press conference with German Chancellor Angela Merkel in Baden-Baden, a German spa town where the summit was due to begin on Friday evening before moving to Strasbourg in France on Saturday.

He said there was no need for Germany to be anxious about the reforms the alliance was about to undertake, specifically referring to its role in Afghanistan.

Germany has been a stalwart NATO ally from the start of this conflict, he said, contributing troops and resources.

Merkel noted that Germany had a "huge responsibility," and said "we will face up to this responsibility in military terms as well."

Germany has balked at sending more troops to Afghanistan, where the NATO-led International Security Assistance Force is fighting the Taliban and helping with civil reconstruction efforts.

The joint efforts of NATO members in Afghanistan need to be bolstered to make the alliance more effective there, Obama said.

"We will all now have to make additional and sustainable efforts to succeed ... Our role is not to occupy Afghanistan," but to prevent it from becoming a safe-haven for terrorists.

"If we discover that the approach we are taking is not effective, it's not working, then we will change it."

He said NATO partners must also work more effectively with Afghanistan's neighbour Pakistan in order "to root out safe havens for extremists."

The two leaders also praised the outcome of Thursday's G20 summit of leading economies in London, which mapped out a fiscal and regulatory plan to revive the flagging world economy.

"None of us can isolate ourselves from a global market, Obama said. "If we do not have concerted action then we will have collective failure."

Before the talks, Merkel rolled out the red carpet for Obama after he flew in by helicopter from Strasbourg, where he met earlier with French President Nicolas Sarkozy.

Strict security measures were in force for the visit, Obama's first to Germany since his inauguration as president in January.

Police said 500 protesters took part in an anti-NATO rally on Friday afternoon. The peaceful protest was held on the outskirts of Baden-Baden after a court banned demonstrations in the city centre. (dpa)