German Foreign Minister Frank-Walter Steinmeier on Tuesday spoke out against Russia’s decision to prepare to deliver missile systems to Iran, Reuters reported.

Speaking before a meeting of G7 foreign ministers in the northern German city of Luebeck, Steinmeier said that it was “too early” to think about rewarding Iran.

“We’re in the middle of a process,” he was quoted as having told reporters. “I’ve told some U.S. senators that they should not now try to unnecessarily impede further negotiations. But I’ll also say that it is also too early to talk about rewards at this stage.”

The Kremlin confirmed earlier Tuesday that an oil-for-goods barter deal between Russia and Iran was being implemented and officials said the road was clear for Moscow to supply an advanced S-300 anti-missile system to Tehran.

Russia signed a contract in 2007 to supply Iran with five S-300 advanced missile batteries, which can be used against aircraft or guided missiles, at a cost of $800 million.

In 2010, Russia’s then-president Dmitry Medvedev cancelled the deal, after the United States and Israel applied strong pressure on him. Both countries worry that the S-300 would make Iran less vulnerable to attack by either one of them, and motivate Iran to develop a nuclear weapon.

Steinmeier’s comments against the Russian decision came as Prime Minister Binyamin Netanyahu called Russian President Vladimir Putin and expressed Israel’s great concerns over the deal, warning Putin that the sale will increase Iran’s aggression in the region and shake the security of the Middle East.

For its part, the United States has responded to the lifting of the ban with statements of concern and admonition, while Iran touted the deal as being good for “regional stability”.