Tokyo: Japan's new Prime Minister Fumio Kishida and US President Joe Biden held their first telephonic call since the former took office, during which they agreed to cooperate to realise a free and open Indo-Pacific region.

Following the phone call, Kishida told reporters that Biden reaffirmed the Senkakus, a group of uninhabited islets in the East China Sea, fall under the Japan-US security treaty, Kyodo News reported.

Kishida took office as Japan's prime minister on Monday. It was his first phone talks with a foreign leader since taking office.

Japan controls the Senkaku Islands, however, China and Taiwan continue to claim them. Tokyo maintains the islands are an inherent part of its territory as per history and international law.

Article 5 of the Japan-U.S. security treaty states Washington will defend territories under Tokyo's administration from armed attack.

"(Biden) gave me strong words of commitment to the defence of Japan," Kishida said.

Meanwhile, a White House readout said that Biden noted that looks forward to strengthening the relationship in the years ahead.

The White House said Biden "noted that he looks forward to strengthening the relationship in the years ahead given the critical role our countries play in advancing our common vision of a free and open Indo-Pacific region, including through the Quad."

The Indo-Pacific region is largely viewed as an area comprising the Indian Ocean and the western and central Pacific Ocean, including the South China Sea.

While Beijing claims sovereignty over almost the entire South China Sea and has overlapping territorial claims with Brunei, Malaysia, the Philippines, Vietnam and Taiwan.

China's territorial claims in the South China Sea and its efforts to advance into the Indian Ocean are seen to have challenged the established rules-based system.