WASHINGTON (REUTERS) - The US military said on Tuesday (Dec 11) it successfully tested a key missile defence system, a milestone that demonstrated US capability to knock down an incoming, intermediate-range missile from countries like North Korea.

The Aegis ashore system used in the latest test was fitted with a Standard Missile 3 Block IIA (SM-3 IIA) interceptor being developed in a joint venture between Raytheon Co and Japan's Mitsubishi Heavy Industries Ltd.

Missile Defence Agency (MDA) Director Lieutenant General Sam Greaves said the successful test was significant.

"(It) was of great significance to the future of multi-domain missile defence operations and supports a critical initial production acquisition milestone for the SM-3 Block IIA missile programme," Lt Gen Greaves said.

In the recent test, a US Air Force C-17 launched an intermediate-range ballistic missile and the interceptor was launched from the Pacific Missile Range Facility at Kauai, Hawaii, the MDA said.

In October, the US military said it successfully tracked and intercepted a medium-range ballistic target missile.

In August, the Pentagon was given the mandate to pursue more options for defeating US-bound North Korean missiles by using radar and more missiles to spot and shoot down inbound threats.

The military has been exploring whether the United States can add another layer of defences to those already in place for intercepting incoming missiles.

The SM-3 IIA is expected to be equipped on US Aegis ashore stations in Romania and Poland.

The Polish section of the defence shield is expected to be operational in 2020. The United States switched on the missile shield in Romania in 2016, which has angered Russia.

Earlier this month, the United States delivered Russia a 60-day ultimatum to come clean about what Washington says is a violation of an arms control treaty that keeps certain missiles out of Europe.

In 2017, Japan decided it would expand its ballistic missile defence system with US-made ground-based Aegis radar stations and interceptors in response to North Korean rockets.