LUEBECK, Germany (AP) — Germany's foreign minister said Tuesday 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 to reporters shortly before welcoming his counterparts from the Group of Seven powers to a meeting in the northern German city of Luebeck.

Asked about the Russian decision, Steinmeier said negotiators were still "in the middle of a process" of trying for a final deal with Iran.

"It is too early to offer rewards," he said.

Steinmeier also urged U.S. senators not to obstruct further talks, saying he hoped that the "constructive" spirit which helped broker a preliminary deal would prevail. U.S. Secretary of State John Kerry's arrival in Luebeck was delayed by a day as he met with lawmakers in Washington on Tuesday to press for time to reach a robust final deal with Iran.

There is a June 30 deadline for a final deal and Steinmeier said that's when it will be possible to say how economic relations with Iran would develop.

Aside from Iran, the G-7's top diplomats will discuss the conflicts in Ukraine and the Middle East, and efforts to improve maritime security.

Steinmeier said he hoped Russia might be brought back into what was previously the G-8, because this would make it easier to resolve other crises around the world. Moscow was ejected from the group last year over its support for separatist rebels in eastern Ukraine.

Steinmeier said he doubted that any of the current conflicts would be solved before Germany hosts the G-7 heads of government for a summit in June.