G20 powers geared for summit talks on Friday in a deserted Argentine capital, after an incident-packed buildup dominated by controversies pitting US President Donald Trump against Russia and his combative stance on trade and climate change.
With Buenos Aires on security lockdown, Trump along with the Russian and Chinese presidents were among the world leaders gathered against a backdrop of tensions surrounding also the Ukraine conflict and relations with Saudi Arabia.
On the G20 margins, Trump scored one victory for his "America First" agenda with the signing of a successor to the North American free trade pact NAFTA, the US-Mexico-Canada Agreement (USMCA).
Although the new pact inherits key features from the old one, Trump has declared it a victory for the US workers he claims were cheated by NAFTA and on Friday called it the most "modern and balanced agreement in history."
"This is a model agreement that changes the trade landscape forever," Trump said at the signing ceremony in Buenos Aires.
The landscape was more rocky on the Russia front.
Trump abruptly cancelled a planned meeting with President Vladimir Putin, citing Russia's recent seizure of three Ukrainian ships, but remains billed to dine with President Xi Jinping on Saturday after igniting a trade war with China.
The US president began Friday with another Twitter blast defending his past business dealings in Russia, a day after his ex-lawyer pleaded guilty to lying to Congress in the context of an investigation into allegations that Putin's government meddled to help elect Trump to the White House.
If Ukraine was the stated reason to cancel his talks with Putin, the latest revelations in the probe showed that Trump cannot escape the lengthening shadow of what he again called the "witch hunt" at home when he comes to international fora like the G20.
Putin jetted into Buenos Aires Friday morning, and the Kremlin said it "regrets" Trump's decision to scrap the meeting.
Amid the Ukraine crisis, European Union president Donald Tusk said he was "sure" that the EU would roll over its sanctions on Russia next month.
And on the G20 front, he admitted the world was undergoing a "difficult moment" overall.
Protesters have vowed a mass rally later Friday as Argentina endures a crippling economic crisis, underlining security concerns after recent football violence forced the relocation of a showpiece final to Spain.
But the government is vowing zero tolerance of any unrest, and declared a public holiday for Friday, shuttering the metro system and keeping the normally choked roads largely free of traffic.
"The summit seems a nonsense to me," call center worker Agustina Vianello, 25, told AFP.
"We are in a bad situation, and we're putting a pile of money into this? Everything's high security. It's strange to see everything so empty," she said.
Trump has cast his talks Saturday with Xi as a deadline for China to cave on his key trade concerns, including access for US companies and protection of their intellectual property.
The US leader has slapped USD 250 billion in tariffs on the world's second-biggest economy and threatened more to come in January.
German Chancellor Angela Merkel meanwhile was to miss the summit's opening after her plane was forced to make an emergency landing in Cologne due to what she called a "serious" technical problem.
She eventually took off on a flight from Madrid bound for Buenos Aires on Friday.
Her temporary absence could complicate French President Emmanuel Macron's attempts to build a European front against Trump at the G20.
Macron on Thursday rejected those who wish to confront economic challenges by being "bellicose, isolationist and closing down borders."
Among the other leaders at the summit will be Saudi Crown Prince Mohammed bin Salman, the focus of tensions over the murder of one of his prominent critics in October.
Macron said he would raise the killing of journalist Jamal Khashoggi with the crown prince on the sidelines of the summit.
G20 sources said climate change was emerging as the biggest stumbling block to agreement on a joint communique when the summit concludes on Saturday.
Trump has yanked the United States out of the landmark Paris climate accord. His opposition to collective action stands in defiance of scientists' increasingly urgent warnings that policy action is desperately needed to counter the climate threat.
With a major UN meeting on climate change starting next week in Poland straight after the G20, UN chief Antonio Guterres said in Buenos Aires that "this is a make-it-or-break-it moment."
US objections on climate and trade have seen two major summits this year, of the Group of Seven democracies and the Asia-Pacific Economic Cooperation forum, end without the once-routine statements.
"Will we even have a (G20) communique? It really is an open question," said former Canadian negotiator Thomas Bernes, a senior fellow at the Ontario-based Centre for International Governance Innovation.
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