A week before the P5+1 group of world powers and Iran are due to start transforming last month's Lausanne framework agreement into a comprehensive nuclear deal, more and more obstacles are popping up in their path.
After two weeks in which discrepancies between the US and Iranian versions of the Lausanne talks kept on surfacing, this week President Barack Obama was forced to compromise with the Republican-controlled Congress on a process that will potentially allow US lawmakers to block the deal.
However, it was Russian President Vladimir Putin who launched the real bombshell.
On Monday, the Kremlin announced that Mr Putin had removed previously imposed restrictions on shipping the S-300 air-defence system to Iran. The advanced ground-to-air missiles were ordered, and partially paid for, by Iran eight years ago and ever since have been the subject of intense controversy. The S-300, capable of intercepting airborne targets up to 150 miles away, would be a significant obstacle facing any country attempting a strike on Iran's nuclear installations. In 2010, Russia agreed to suspend the supply of the missiles as part of the international pressure on Iran to limit its nuclear development.
The decision this week to remove the restrictions was explained by the Kremlin as a move "in the spirit of good will to promote progress at the talks". However, other countries - including the US and France, which remonstrated with Moscow - see it as a unilateral step by the Russians to break the international sanctions regime on Iran before a comprehensive deal has been signed.
The Russians insisted that the S-300 was "a completely defensive weapon" and its supply did not contravene the sanctions. This was Mr Putin's message to Prime Minister Benjamin Netanyahu, who called the Russian leader on Tuesday to protest that the missile sale "will jeopardise the security of the Middle East".
Jerusalem officials stressed that their immediate concern is that the Russian announcement signals a crumbling of the sanctions. It is less clear at this point how the S-300 could affect a potential Israeli or US attack. The S-300 is a formidable system but the Russians have yet to specify when they plan to ship it to Iran and it would take many more months before it could become fully operational. Even then, the Israelis and Americans are already well acquainted with the S-300, which is used by a number of Western allies, and have had ample time to devise tactics to evade it.