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 in security fields," a government document said after the rule was approved by the Cabinet on Friday.

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 have 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", a national security official in the prime minister's cabinet told AFP prior to the Cabinet approval.

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

"Theoretically, the new rule will enable export" of the PAC3 to the United States, the official 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, and South Korea has quietly pledged to provide hundreds of thousands of rounds of artillery ammunition to Kyiv over the past year, the newspaper said.

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 ($20 billion) annually -- less than some individual US defence contractors' yearly revenues.

Government also approved on Friday a record defence budget worth $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.