The leaders of Japan, the United States, Australia and India, which form the framework known as Quad, are believed to have agreed to reinforce their security cooperation to realize a free and open Indo-Pacific region. This comes amid China's growing maritime assertiveness.

The leaders wrapped up their summit hosted by US President Joe Biden in his home state of Delaware on Saturday. The other attendees were Japanese Prime Minister Kishida Fumio, Australian Prime Minister Anthony Albanese and Indian Prime Minister Narendra Modi.

Kishida said at the start of the talks that the security environment is becoming increasingly severe, while the international order based on the rule of law is under threat.

He said it is pivotal for the Quad countries, which share values such as freedom and democracy, to continue demonstrating to the international community their steadfast commitment to a free and open Indo-Pacific.

Kishida added that Japan wants to advance practical cooperation while listening to voices of ASEAN and South Asia as well as Pacific island countries.

Biden said the Quad nations are democracies that "know how to get things done." He said that is why in the first days of his presidency he reached out to them to propose they "elevate the Quad" to make it "more consequential."

Biden emphasized that four years later the four countries "are more strategically aligned than ever before."

On top of security cooperation, the leaders are also believed to have affirmed that they will work together across a broad array of spheres.

The expected areas of cooperation range from cybersecurity and the development of important and emerging technologies to disaster relief and global health, such as anticancer programs.