Japan loosened arms export controls on Friday to enable it to sell domestically made Patriot missiles to the United States, which is seeking to stock up after sending the weapon systems to Ukraine.

Washington has supplied Kyiv with the highly-effective Patriot air defence systems as part of the massive Western military aid effort to help President Volodymyr Zelenskyy's country fight back against Russia.

"We welcome the Government of Japan's announcement today that it will transfer Patriot interceptor missiles to the United States to replenish US inventories," the White House said in a statement.

Japan produces the PAC3 surface-to-air missile defence system, paying a licence fee to US defence firm Lockheed Martin which developed the system.

Japan strictly controls the export of arms under its pacifist constitution, which limits its military capacity to ostensibly defensive measures.

"The appropriate transfer of defence equipment overseas will contribute to... international peace and security, and will also strengthen cooperation with allies and the US," a Tokyo government document said after the rule was approved by the Cabinet.

Sales of the Patriot Advanced Capability-3 (PAC3) system to the United States would be Japan's first export of lethal arms since the end of World War II, local media reported.

With the new rule Japan "will be able to export arms which were domestically produced under licence of a foreign company to the licensing country", an official in the prime minister's cabinet said.

A senior ruling party official told reporters this week that the export plan was at the request of Washington, Kyodo News reported.

US President Joe Biden raised the issue with Prime Minister Fumio Kishida at a meeting at Camp David in August, as well as during an economic summit in San Francisco last month, The Washington Post reported this week, citing unnamed US officials.

Washington is increasingly looking to its allies to supply sophisticated weapons against the backdrop of a shortfall in Ukraine's air defences, with South Korea quietly pledging to provide hundreds of thousands of rounds of artillery ammunition to Kyiv over the past year, the newspaper said.

The White House added that Friday's decision "will contribute to the security of Japan and to peace and stability in the Indo-Pacific region by ensuring that US forces... will continue to maintain a credible deterrence and response capability."

Japan used to ban all exports of defence equipment but in 2014 the late prime minister Shinzo Abe's cabinet loosened the rules.

The country's defence industry is small, with the only customer being the Japanese military and the market estimated at around 3 trillion yen (US$20 billion) annually – less than some individual US defence contractors' yearly revenues.

The government also approved on Friday a record defence budget worth US$56 billion for the next fiscal year, in line with Kishida's goal of doubling defence spending to the Nato standard of two percent of GDP by 2027. (AFP)