Hamburg, Germany (CNN) World leaders at the G20 summit in Germany went into their final day of talks Saturday scratching their heads over what to do about a increasingly isolationist United States.

Leaders appeared to be at an impasse over trade and climate change, with German Chancellor Angela Merkel making clear that the US' stance on the key issues were threatening to derail progress and that talks had been difficult.

US President Donald Trump won the 2016 election on an "America First" platform that would pull the United States out of several multilateral trade deals and negotiations, as well as the landmark Paris Agreement on climate change.

Merkel illustrated an everyone-versus-the-US scenario late Friday, and said leaders were considering how they could now present these markedly different stances in one communique.

Trans-Atlantic trade war?

Merkel criticized Trump's protectionist trade policies, saying that "virtually everyone believes we need free but also fair trade."

"However, I can foresee that the sherpas have a lot of work ahead of them tonight to hammer out the communiqué on trade, and I hope that they will present us with a good result tomorrow. But I don't want to beat about the bush, the discussions are very difficult."

Key to the trade impasse is the suggestion that the US might impose tariffs on steel imports.

European Commission President Jean-Claude Juncker said the EU would react to steel tariffs perhaps even with their own, giving early warning signs of a trade war.

"We've got to look at protection when it comes to steel imports. It's necessary for the EU to react in an adequate and appropriate way when it comes to steel. We've got to take measures to ensure that we act properly when it comes to imports from other parts of the world," Juncker said.

"I cannot go into details now, but we will react. We will take counter measures in the hope that all of this will not be necessary."

Trump talks climate

Trump faced a chorus of global outrage last month when he announced he was withdrawing the US from the Paris climate accord.

"As you know, almost everyone is committed to the Paris Agreement," Merkel said.

"But it will also be very interesting to see how we word the communique tomorrow and make it clear that there are, of course, differing opinions on this topic, because the US has sadly withdrawn, or wants to withdraw, from the Paris Agreement, and that is obviously playing a part in our discussions."

She said, however, that Trump had taken part in climate talks and that leaders were now working out how to organize such differing opinions.

Talks between Emmanuel Macron, Trump and several other leaders on climate change delayed the French President for his meeting with Putin, who seemed to mock the leaders over the impasse.

"Well, I hope now the climate will be better," he laughed when Macron apologized for being late. "I'm sure that now you've discussed it, everything will be fine."

Trump-Putin showdown

Much of the attention at the G20 has been on a bilateral meeting between Trump and Putin. The two leaders met officially for the first time on Friday but gave little away about the nature of their discussions.

Secretary of State Rex Tillerson, the only American official in the room apart from Trump, told reporters that the President had raised the issue of Russia's alleged interference with the 2016 US election, in what he described as "robust and lengthy exchange."

Russia set out its version of events, saying that Trump accepted Putin's statements that the Russian government did not interfere in the election. This account is at odds with Tillerson's.

Putin is expected to speak again on Saturday, and reporters and leaders will be listening carefully to his remarks to establish any shifts in the US-Russia dynamic.

Trump met with British Prime Minister Theresa May on Saturday and said he expected the two nations to ink a "powerful" trade deal soon . The UK is not able to sign such a deal until it finishes talks with the European Union to pull out of the regional bloc, talks that are likely to end in 2019.

Trump also began meeting with Asian leaders, and will sit down with Chinese president Xi Jinping, where he will no doubt discuss North Korea's uptick in missile testing activity and the role Beijing could play in calming the rogue state.

The G20 summit has been marked by violent protests against capitalism, globalization, climate change and the concentration of power among the 20 nations.

The Hamburg Police press office said that more than 200 police officers have so far been injured and that 114 people have been arrested. Another 89 have been taken into temporary custody. It was not clear how many protesters were injured. Around 1,000 police officers have arrived in Hamburg to support security forces.