JERUSALEM, May 1 (Reuters) - A planned live test of Israel's Arrow-3 ballistic missile interceptor in the United States has been postponed to improve the system's readiness, the Israeli Defence Ministry said on Tuesday.

Jointly manufactured by Boeing Co (BA.N) , Arrow-3 is billed as capable of destroying missiles in space, an altitude that would destroy any non-conventional warheads safely. Israel regards it as a bulwark against Iran and Lebanon's Hezbollah.

No new date was given for the live test. The system passed its first full interception test over the Mediterranean sea in 2015 and was deployed in Israel in 2017.

Israel had planned another test in the summer of 2018 in Alaska, whose expanses would have allowed larger interception distances.

The Defence Ministry statement said the postponement had been agreed upon with the Pentagon, which is Israel's partner in the Arrow system development, "with the goal of reaching maximum readiness for a test on the American range".

The operational capacity of Arrow-3, and earlier generation Arrow-2 units also deployed in Israel, was unaffected, it said.

Israel has had difficulties with its Arrow-3 tests.

Its first full trial, scheduled in 2014, was aborted due to what designers said was a faulty flight by the target missile. Follow-up Israeli tests last December and January were also called off at short notice due to technical problems.

Arrow serves as the top tier of an integrated Israeli shield built up to withstand various potential missile or rocket salvoes. The bottom tier is the already deployed short-range Iron Dome interceptor, while a system called David’s Sling, due to be fielded next year, will shoot down mid-range missiles.