"We can see the top of the mountain but we are not quite there yet," the minister said upon his arrival at Beau Rivage Hotel, where the talks are underway.
"The last meters are most difficult, yet possible, and this is what we are talking about in the last hours and days," he underscored.
Steinmeier said he hoped that Tehran will not give up its efforts to reach a viable agreement.
Later in the day, the German foreign minister is expected to attend a working lunch with his US and French counterparts, John Kerry and Laurent Fabius.
The talks to ensure that Iran's nuclear program is solely for peaceful purposes restarted on Thursday amid increased pressure on negotiators to hammer out a framework deal ahead of the March 31 deadline.
Iran and the group of P5+1 – France, Britain, Russia, China, the United States and Germany – agreed last year to finalize a comprehensive deal on Tehran's nuclear program by July 2015.
