Japan's Prime Minister Shinzo Abe reacts during a budget committee session of the upper house at parliament on Thursday in Tokyo. Photo: AFP

Japan "can't move ahead" with a costly US missile defense system, Prime Minister Shinzo Abe said Tuesday, throwing his support behind a decision to suspend deployment of the controversial program.

In a surprise announcement a day earlier, Japan's Defense Minister Taro Kono said the deployment of the Aegis Ashore system would be suspended, citing cost and time constraints.

Abe's comments appear to suggest the system, which was originally estimated to cost Japan $4.2 billion over three decades, may be scrapped altogether.

The government had originally guaranteed that interceptor missile gear would not land in residential areas near where the system was based. 

But Kono said his ministry concluded that maintaining that promise would require a costly and time-consuming hardware upgrade.

But he said the government was committed to considering alternatives.

The Aegis Ashore radar purchase, approved in 2017, was seen both as part of attempts by Tokyo to bolster its defensive capabilities, and as a way to foster closer ties with Washington. 

US President Donald Trump has pushed allies to buy more American products including military equipment.

Japan's military has long been restricted to self-defense and the country relies heavily on the US under a bilateral security alliance.

The purchase has been controversial. Residents in the regions where the system was to be deployed have argued that the interceptor could affect residential areas, and voiced concerns that they could become targets in a conflict.

AFP