Iran recently test fired a two stage, solid fuel ballistic missile, the Sejil II. This missile has a range of 2,000 kilometers, and can reach Israel. Iran already has dozens of liquid fuel missile with the same range, the Shahab 3. What makes the Sejil II more dangerous is the fact that it can be fired on short notice. The Shahab 3 takes several hours to get ready, as the liquid fuel must be pumped into the missile. Israeli spies and photo satellites can spot the Shahab 3s being fueled, allowing the Israeli anti-missile systems to be placed on a higher degree of readiness. This makes it more likely that the Iranian missiles would be intercepted.
The Sejil II is not really a surprise. A year ago, Iran tested a new IRBM (Intermediate Range Ballistic Missile) called the Sejil. This was a solid fuel missile. Two years ago, Iran had a failed test of a solid fuel ballistic missile it called "Ashura." The Sajil appeared to be the Ashura with a new name, and modifications that make it work. Even then, the big question was, who did they get the solid fuel manufacturing technology from? There are many potential vendors (North Korea, Pakistan, Russia, China, or even stolen from the West). The Ashura test failure last year involved some problem with the second stage, not with the solid fuel rocket motors. Iran has been manufacturing solid fuel for smaller rockets for over a decade, but had not yet developed the technology to build larger, and reliable, solid fuel rocket motors. Israel believes that Iran got the advanced solid fuel technology from Pakistan.
For the last five years, Iran has been producing Shahab 3 IRBMs. This missile is basically 1960s technology, with the addition of GPS guidance. Russian and North Korean missile technology has been obtained to make the Shahab 3 work. This has resulted in a missile that apparently will function properly about 80 percent of the time, and deliver a warhead of about one ton, to a range of some 1,700 kilometers, to within a hundred meters of where it was aimed. By world standards, this is a pretty effective weapon. A solid fuel version of this missile would be, if the solid fuel was of reasonable quality, about ten percent more reliable than liquid fuel, and easier to hide and launch.
Iran has continued to refine the Shahab 3 design, and conduct test firings. Iran is believed to have 50-100 Shahab 3s, and is building about one a month. Israel appears to be the main target. Iran has threatened Israel with destruction, rather openly and for several years. Shahab 3's could be fired with high explosive warheads, and hit, with enough accuracy, to kill mostly Jews, and not Israeli Arabs or Palestinians.
Israel has threatened to retaliate with nukes if Israel is hit with chemical or nuclear warheads. Israel has Arrow anti-missile systems that can stop Shahab 3s, but only a few at a time. If Iran launched a dozen or more Shahab 3s simultaneously, some would get through. If Iran had several hundred Shahab 3s, they could launch most of them at Israel, using high explosive warheads, and do a lot of damage. Israel could respond with its own Jericho II missile, but this system was designed for use with nuclear weapons, and Israel apparently only has 20-30 of them. Israel could respond with air strikes, and cruise missiles from submarines in the Persian Gulf or Indian Ocean. But, again, this would appear as a limited response to massive Iranian missile attacks. An Iranian attack with nuclear warheads would kill a large number of Moslems, and even radical Iran might be put off by that, because Israel would likely respond in kind.
A large number of IRBMs could also be used to intimidate nearby Arab countries, as these missiles could damage oil production facilities. If Iran gets nuclear weapons, it would take 5-10 years to develop the complex engineering required to create a nuclear warhead that would survive the stresses of missile launch, and detonate as intended over a distant target. Russia or China might provide such engineering secrets, but given the warlike pronouncements and radical politics of the Iranians, probably not.