Israel plans to invest $1 billion in the development and production of batteries for its Iron Dome rocket interception system, a top Israeli defence official said in an interview published Monday.

Defence Ministry director-general Major General Udi Shani told the daily Haaretz newspaper that five countries have already expressed interest in the system, which was successfully deployed during a rise in rocket fire from Gaza in early April.

But Shani, in his first interview since his appointment in January 2010, warned that the system's capacity must be put in perspective.

"We need to adjust expectations in relation to Iron Dome," he told Haaretz.

"We have (accomplished) a significant achievement in reaching operational capacity sooner than expected, but this is not a system that can ensure the interception of every rocket in every situation."

Shani said Israel would invest heavily in the system, which is developed by the Haifa-based Rafael Advanced Defence Systems, in addition to receiving US funds to boost Iron Dome's capacity.

"We are talking about (having) 10-15 Iron Dome batteries. We will invest nearly $1 billion in this. This is the goal, in addition to the $205 million that the US government has authorised," he said.

Shani did not specify the length of the period over which the investment would be spread.

Israel deployed the first battery of the unique multi-million dollar system on March 27 outside the southern desert city of Beersheva, after it was hit by Grad rockets fired from Gaza.

On April 4, the system was also deployed around the southern port city of Ashkelon.

The system, the first of its kind in the world and still at the experimental stage, is not yet able to provide complete protection, but it successfully brought down a number of rockets fired from Gaza in April in what was the first time it had been used in an actual combat scenario.

Designed to intercept rockets and artillery shells fired from a range of between four and 70 kilometres (three and 45 miles), Iron Dome is part of an ambitious multi-layered defence programme to protect towns and cities.

Two other systems make up the programme -- the Arrow long-range ballistic missile defence system and the so-called David's Sling or Magic Wand system, which is intended to counter medium-range missiles.

Shani said Israel plans to invest another $1 billion in David's Sling over five years, and that the system should have its first operational capacity by 2012.