The United States’ $36 billion system of ground-based interceptors can’t yet be counted on to shoot down a nuclear-armed missile aimed at the West Coast by North Korea or Iran, the Pentagon’s weapons testing office says.

The network of radar and communications combined with missiles based in California and Alaska has demonstrated only a ‘‘limited capability to defend the US homeland from small numbers of simple’’ intercontinental ballistic missiles, the testing office said in its latest annual report.

Despite international sanctions, North Korea has continued to test nuclear bombs and the missiles that might eventually carry a miniaturized warhead to the continental United States. Meanwhile, US officials have also criticized Iran for conducting ballistic missile tests, although the Islamic Republic has said its program is defensive and isn’t designed to carry nuclear warheads.

The probability that the United States would succeed in intercepting an incoming missile can’t be quantified with any precision ‘‘due to a lack of ground tests’’ supported by verified ‘‘modeling and simulation,’’ according to an advance copy of the assessment provided late Monday to congressional defense committees and Pentagon officials.

Bloomberg News