Host president, Argentina's Mauricio Macri, said the solution was "dialogue, dialogue and dialogue" and called for a clear message of shared responsibility.

But US President Donald Trump has already cancelled meeting Russia's Vladimir Putin over Ukraine.

And huge differences remain on climate change, trade and the Khashoggi affair.

The G20, made up of 19 of the world's most industrialised nations plus the EU, accounts for 85% of the world's economic output and two-thirds of the world's population.
Its meetings, which began in 2008, are an opportunity for members to develop global policies tackling major issues - but many of the key decisions will be made in one-on-one encounters.

There is massive security for the summit in Buenos Aires, with a bank holiday declared for Friday and the city's main business district shut down.

Protesters angry at the money spent on the summit while Argentina struggles through tough austerity demonstrated outside the meeting.

What have the opening exchanges told us?
The world leaders were all called on to the stage and assumed their position for the traditional family photograph.
Saudi Crown Prince Mohammed bin Salman stood on the outside of the photo, far away from Turkey's Recep Tayyip Erdogan.

This is the crown prince's first major diplomatic test since the murder in Turkey of Saudi journalist Jamal Khashoggi, a key critic of the government. Saudi Arabia has blamed "rogue agents" but suspicion has fallen on the prince for ordering the killing.

After the photo was taken, the crown prince did manage a hearty exchange with Mr Putin.

French President Emmanuel Macron held a five-minute exchange with the crown prince during which, a French official said, Mr Macron had conveyed "very firm" messages over the Khashoggi affair.

BBC