U.S. negotiators blocked progress at the Group of 20 summit on managing migration, slowing climate change, and streamlining how world trade is governed, according to European officials involved in the discussions.

Security concerns also weighed on the two-day talks in Buenos Aires. Argentina's security minister said eight gasoline bombs were discovered in an area of the capital several miles from the summit venue where a protest in the afternoon drew thousands of demonstrators who held up banners with slogans like "Go away G-20" and "Go away Trump."

The whole point of the G-20 — formed in the wake of the global financial crisis a decade ago — is finding ways to solve global problems together, but diplomats in Buenos Aires struggled to find enough things all the leaders agree on.

Trump sought to use the summit to make his own trade deals, and angered the Argentine hosts by misconstruing their position on China's trade practices.

Meanwhile, two men under heavy criticism from the West lately — Russian President Vladimir Putin and Saudi Crown Prince Mohammed bin Salman — appeared to seek refuge in each other, bonding with a tough-guy hand grab as the leaders sat down around a huge round table for talks.

Argentine President Mauricio Macri kicked off the summit by acknowledging divisions within the G-20 while urging world leaders to have a "sense of urgency" and take actions "based on shared interests."

Diplomats from the Group of 20 countries were haggling hard over a final summit statement, with deep divisions over what language to use on the Paris climate accord and the World Trade Organization.

Two European officials involved in the discussions said the U.S. was stymieing progress on both.

So an unorthodox solution emerged: An official in the French president's office said the statement may have language that sets the U.S. apart. For example, a draft says 19 of the participants agree on the importance of upholding the Paris climate accord, but the U.S. doesn't.

Asked about the European concerns, a U.S. official said progress was being made on the joint statement and the White House was "optimistic" about the document as a whole.

Later the Argentine official shepherding the G-20 finance talks, treasury official Laura Jaitman, said Trump was "very active and committed" in the dialogue and said progress was made in Friday's talks on finance and trade.

"There's a very positive message of how trade has been an engine of growth for the next decades and how it will continue in the future providing benefits for all citizens," Jaitman said.

Argentine Foreign Minister Jorge Faurie said trade talks were moving forward and nations were continuing to work on climate change wording.

Despite Trump's dismissal of concerns about global warming, China, France and the United Nations came together Friday to pledge their support for the Paris climate accord. Their declaration was meant to encourage other G-20 members to do the same, and to provide a boost for an upcoming U.N. climate summit.

Overall the G-20 summit is meant to focus on issues such as labor, infrastructure, development, financial stability, climate sustainability and international commerce.

But as the gathering got underway, those themes seemed like afterthoughts, overshadowed by contentious matters from the U.S.-China trade dispute to the Russia-Ukraine conflict.

Russia and Ukraine have traded blame over the weekend seizure of Ukrainian ships and their crew — which Trump cited in canceling a much-awaited meeting with Putin at the G-20. Russia's foreign minister regretted the cancellation, but said "love can't be forced."

Also looming large amid dozens of bilateral meetings in Buenos Aires: The gruesome slaying of dissident Saudi journalist Jamal Khashoggi in Saudi Arabia's Istanbul Consulate and how the Saudi crown prince, who is alleged to have ordered the killing, is received by world leaders.

As soon as he arrived, the crown prince was confronted by French President Emmanuel Macron, who pressed him on the Khashoggi investigation and the Saudi-backed war in Yemen.

Bin Salman told Macron not to worry, but Macron countered, "I am worried."

Saudi Arabia has denied that bin Salman played a role, but some leaders were concerned about seeming to legitimize a man who U.S. intelligence agencies concluded ordered the killing. Trump's administration, however, has made clear it does not want to torpedo the longstanding U.S. relationship with Riyadh.

It is the prince's first significant appearance overseas since the killing. Turkish President Recep Tayyip Erdogan, who has been sharply critical of Saudi Arabia over the incident, is also in attendance.

Leaders of the United States, Canada and Mexico, meanwhile, met in the morning to sign a trade deal replacing the North American Free Trade Agreement that was struck following months of tough negotiations that analysts say left a bitter taste among the partners.

It must still be ratified by lawmakers in all three countries, and passage in the U.S. could face a tough road in the House of Representatives after Democrats won a majority in November midterm elections.

While Trump canceled his meeting with Putin, the U.S. president was still scheduled to meet with Chinese President Xi Jinping, but analysts were not optimistic about prospects for a major breakthrough on the two countries' trade disputes a month before U.S. tariffs on Chinese goods are set to ramp up.

German Chancellor Angela Merkel arrived late after her plane suffered a technical problem.

British Prime Minister Theresa May's attendance at the summit marked the first time a U.K. prime minister has visited Argentina's capital. The only other prime minister to visit the country was Tony Blair, who went to Puerto Iguazu in 2001. The two countries have long been at odds over the South Atlantic islands known as the Falklands in Britain and the Malvinas in Argentina.

Faurie, the Argentine foreign minister, said the recent establishment of more flights to the disputed islands was a positive development.

"We are not withdrawing our historic claim," he added. "The focus of this opportunity is in the reestablishment of trust."

In downtown Buenos Aires, meanwhile, thousands of demonstrators flooded the 9 de Julio Avenue waving flags and holding up banners. Several marched topless with colorful national flags of summit countries painted on their chests."

About 22,000 police officers and other security forces are guarding the leaders during the summit.

Argentina is the first South American country to host the G-20, and officials have the added challenge of ensuring that chaos is better contained than it was at last year's meeting in Hamburg, Germany, where clashes broke out between police and protesters.

Argentine authorities have said they will not tolerate violence or allow the gathering to be disrupted.