Germany's foreign minister says it's too early to reward Iran for a preliminary agreement on its nuclear program, criticizing Russia's decision to lift a ban on delivery of an air defense missile system.

Frank-Walter Steinmeier spoke as he welcomed counterparts from the Group of Seven powers Tuesday to a meeting in northern Germany. They're expected to discuss Iran, Ukraine and Yemen among other issues.

Asked about the Russian decision, Steinmeier said negotiators are "in the middle of a process" of trying for a final deal with Iran. He said U.S. senators shouldn't try to obstruct further talks "unnecessarily" but "it is also too early to offer rewards."

There is a June 30 deadline for a deal. Steinmeier says that's when it will be possible to say how economic relations develop.