Speaking on the first official day of the two-day G20 summit in Osaka, Abe also said Japan, as a flag-bearer of free trade, would strongly promote improvement in a multilateral trade system and negotiations over agreements on economic cooperation.

"Today, I want to discuss with leaders measures to further enhance momentum towards reform in WTO, (World Trade Organisation)", he said.

The G-20 leaders are meeting at a time of profound tensions over trade, globalization and Iran's collapsing nuclear deal.

US President Donald Trump made it clear he had numerous grievances to thrash out with allies over trade and defence spending.

Russian President Vladamir Putin set off an argument about Liberal values even before his arrival.

Putin told the Financial Times that "the liberal idea has become obsolete. It has come into conflict with the interests of the overwhelming majority of the population."

He praised Donald Trump's stance on migration and said liberalism "presupposes that .... migrants can kill, plunder and rape with impunity because their rights as migrants have to be protected."

European Union President Donald Tusk blasted Putin's comments, telling reporters, "What I find really obsolete are: authoritarianism, personality cults, the rule of oligarchs. Even if sometimes they may seem effective."

Abe has sought to make the Osaka summit a landmark for progress on environmental issues, including climate change.

Japan also hopes to forge agreements on reforms of global finance, especially strengthening precautions against abuse of technologies such as cyber-currencies to fund terrorism and other types of internet-related crimes.

On the rising tensions between Iran and the United States, U.N. Secretary-General Antonio Guterres said the world can't afford the conflict and it was "essential to deescalate the situation" and avoid confrontation.

Iran is soon poised to surpass a key uranium stockpile threshold, threatening the nuclear accord it reached with world powers in 2015.

Australian Associated Press