Shamkhani said the solid fuel increases the range of the missile, IRNA reported.
"Using solid fuel would be more durable and increase the range of the missile," the defense minister told reporters on the sidelines of a seminar on information and communications technology and C4I command and control at Malek Ashtar University.
"The test was a success," the defense minister said on television.
"When you fill a missile with liquid fuel, you have to use it quickly. With solid fuel, a missile can be stored for years. And in addition, it makes the missile more accurate and cheaper too."
A Defense Ministry statement said the new technology could be built into Shahab-3 missiles -- which have a range of at least 2,000 kilometers (1,280 miles).
Military experts contacted by AFP said the test, if indeed successful, would signify an important breakthrough for the Islamic Republic's missile program.
First of all, in order to develop a missile with a range greater than 2,000 kilometers -- in effect a two-stage rocket -- a country needs to master the more complex solid fuel technology.
"The maximum range of a single stage missile is around 2,000 kilometers. In order to send a missile further, you need a twin stage design that separates in mid-flight," said one analyst.
"This separation is very complex, and in order to maintain the accuracy of the missile, it needs to be using solid fuel.
"In very simplistic terms, think of a liquid fuel missile as a bottle of mineral water -- the liquid is sloshing around and makes the bottle unstable," he said.
"And even if the missile is only a single stage design, solid fuel makes it more accurate," he added.
While Shamkhani did speak of a "two motor missile", a Defense Ministry official said that he was only referring to separate launch and flight thrusters of the single-stage Shahab-3.
A second advantage of solid fuel missiles of all ranges is that they are more mobile and can be deployed far more quickly than liquid fuel devices, which need to be filled up in situ before their launch.
In practice, that means the Shahab-3 missiles can now be spread across the country and stored far from any refueling facilities in preparation for immediate deployment.
In a quick reaction to the latest Iranian test, Israel warned the "free world to beware of Iran's plans".
"We are closely monitoring these worrying projects being plotted in Iran," said one senior Israeli official contacted by AFP.
MS/HG
End
MNA