According to Ha'aretz quoted by RiaNovosti "Israel has intensified its efforts to prevent deliveries of Russian S-300 air defense systems to Iran under a 2007 contract".
The question should be: why?
Why should the Israelis want to stop delivery of a defence system? Pretty obvious really. If the Iranians get the S-300 air defence system, the Israelis won't be able to not only threaten Iran, but carry out those threats.
It is important for peace in the ME that Russian delivers the system to Iran as soon as possible.