Steinmeier told reporters on Thursday ahead of a closed-door meeting with Iranian Javad Zarif in Berlin: “We are now in a decisive phase."
He said: "We all agree that we cannot continue with endless extensions."
"Therefore we must really make use of the new window of opportunity. We shall spare no effort to find a solution."
The P5+1 group of powers - the five permanent members of the UN Security Council; the U.S., U.K., China, France and Russia, plus Germany - and Iran have already missed two deadlines for a permanent settlement on Iran's nuclear program.
Negotiations in the Austrian capital, Vienna, on Nov. 24, 2014 were supposed to be the final round of talks between Iran and the group of world powers.
However, the deadline for a permanent settlement was extended until the end of June, 2015.
Steinmeier emphasized that a solution to the crisis should address the concerns of the international community.
“The way for Iran to acquire nuclear weapons must be clearly, verifiably and permanently closed. In return for that sanctions would be lifted step-by-step,” he said.
Steinmeier underlined that it was important to restore trust between the negotiating partners and Iran, not only for a peaceful solution for the nuclear problem, but also to address the new challenges in the Middle East, including the threat posed by Islamic State of Iraq and Levant or ISIL.
Zarif said in a brief statement to journalists ahead of his meeting with Steinmeier that 11 years had been lost in nuclear talks, but there was now a determination to use a "new window of opportunity" to reach a permanent settlement in the final round of nuclear talks.
The multilateral talks with the five permanent members of the UN Security Council - the U.S., U.K., China, France and Russia- plus Germany, also known as the P5+1 group, will start on Jan. 18 in Geneva.
The delegations will hold bilateral talks in Geneva ahead of the multilateral talks.