The leaders of the world gather in Argentina for their annual G20 summit in the midst of new tensions with Ukraine and the US trade dispute with China.
US President Donald Trump has canceled a meeting with his Russian counterpart Vladimir Putin to protest against the Russian occupation of Ukrainian naval boats.
At the incident on the Black Sea 24 sailors were detained.
A massive security operation is underway for the summit in Buenos Aires, Argentina.
For Friday and for the city a holiday was declared Central Business District was closed.
What is spoken at the summit?
Hopes for progress in talks with Chinese leader Xi Jinping expected by Mr. Trump have been dampened.
The two economic giants are trapped in a trade war that may even escalate.
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Climate change promises to be another important issue in the talks.
French President Emmanuel Macron was quoted by the AFP News Agency as saying that he would refuse to sign a trade agreement with the South American Mercosur bloc if Brazilian President Jair Bolsonaro withdrew from the Paris Climate Agreement.
The Summit is also a diplomatic test for Saudi Crown Prince Mohammed bin Salman against the backdrop of ongoing questions about the possible involvement of the Saudi state in the murder of journalist Jamal Khashoggi in Turkey.
What was said about the Ukraine crisis?
Mr. Trump said he would not do it because Putin did not return because the Ukrainian ships and sailors who seized Russia in the Black Sea near the Crimea had not been returned.
The decision also follows the former lawyer of the US President, Michael Cohen, who has pled guilty to Congress for Trump's real estate business in Russia lied during the 201
Chancellor Angela Merkel blames The Crisis "wholly" on Russia and said it will address the issue with Mr Putin. However, the arrival of Mrs. Merkel at the summit was delayed by a technical error in her plane.
The plane had to land in Cologne on Thursday night, and she will not come to Buenos Aires until other leaders have started their talks.
How intense is the trade war?
President Trump recently said that current tariff levels would rise to $ 200 billion (£ 157 billion) of China's imports as planned.
He also threatened with duties on other Chinese exports to the US amounting to $ 267 billion.
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Speaking to White Ho Reporters Englisch: emagazine.credit-suisse.com/app/art…2934 & lang = en China was interested in a deal, "I do not know if I want to do that" and "I like the deal we have now."
The US has received a total of $ 250 billion in Chinese customs duties since July, and China has retaliated by charging US $ 110 billion in tariffs.
"I think the most likely scenario is that [Chinese President] Xi Jinping Trump does not offer enough concessions, and so Not much of the G20 meeting, "said Julian Evans-Pritchard of Capital Economics.
What can Crown Prince Mohammed expect?
International outrage over the killing of Khashoggi on August 2 at the Saudi Arabian consulate in Istanbul October went far on Thursday when Canada imposed sanctions on 17 Saudi citizens allegedly linked to his murder.
British Prime Minister Theresa May has said that she will meet the Crown Prince and deliver a "very clear" message.
"In relation to Mr. Khashoggi, we want a comprehensive and transparent investigation into what happened and those responsible held accountable," she said.
What is the G20?
The group of 20 brings 19 leaders together most of the developed world and the EU.
Argentina, Australia, Brazil, Canada, China, France, Germany, India, Indonesia, Italy, Japan, Mexico, Russia, Saudi Arabia, South Africa, South Korea, Turkey, United Kingdom and the United States are all represented.
The focus of the two-day summit opening on Friday, according to the website of the event, is on "fair and sustainable development".
The last summit in the German city of Hamburg was clouded by violent protests.
In Buenos Aires, where the first G20 meeting is being held in South America, more than 20,000 policemen have been deployed to maintain order.
Bad timing for Argentina's leader
By Katy Watson, South America Correspondent, BBC News
This should be a great moment for Argentina. A chance to show the world leaders that the country was at the forefront of business with Mauricio Macri.
In his election in 2015, Mr. Macri promised market-friendly reforms to bring Argentina's isolated economy back on track.
Three years on and he hosts this summit in a new political era – one in which protectionism and populism rather than globalization are on the agenda.
And while Mr. Macri wants to leave a good impression on his visitors in the next few days, he fights with his reputation, which is closer to his home town.
Inflation is high, economic growth is sluggish, the peso has fallen, and the country has had to rely on a $ 57 billion loan from the deeply unpopular IMF to help free itself from the crisis. It is not a good time for a president to seek re-election next year.
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