In a letter released by his office, Frank-Walter Steinmeier told Clinton he supported her aim of creating a world "with more friends and fewer opponents" and overcoming "hate, violence, lawlessness and despair".

"I would like to offer you my full support for this policy," he wrote.

"Building on solid German-American relations, which have united us in a spirit of close friendship for many years, let us work together to find solutions to the greatest challenges of our time: the conflict in the Middle East, climate change, the Iranian nuclear programme and the financial crisis, just to name a few."

Germany is one of six countries working together in a bid to persuade Iran to abandon its nuclear ambitions. Steinmeier has long called on Washington to consider direct talks with the leadership in Tehran.

At her confirmation hearing a week ago, Clinton told the Senate Foreign Relations Committee that the Obama administration would pursue "an attitude toward engagement (with Iran) that might bear fruit".

But she did not mention whether Washington would set conditions for such a change in US policy after nearly 30 years of official silence with Tehran.