The world's most powerful leaders gathered for the start of the G20 summit in Japan on Friday for meetings that may set the directon for global economy and policies. On the top of the agenda will be indications of a breakthrough in the US-China trade talks and efforts to stem rising tensions in the Arabian Gulf between Washington and Iran. Climate change and the reduction of plastic pollution in the world's oceans will also feature in the two-day summit. The US President Donald Trump will also meet with Russian leader Vladimir Putin and German Chancellor Angela Merkel for talks. Follow the key points and developments as they happen below. British Prime Minister Theresa May took a final jab at Vladimir Putin in a bilateral meeting, but said she was "open to a different relationship" in future. Mrs May, attending her final G20 summit before she steps down, said Russia would have to stop "irresponsible and destabilising activity that threatens the UK and its allies - including hostile interventions in other countries, disinformation and cyber attacks" to improve relations. She said the UK had "irrefutable evidence" that Russia was behind the March 2018 Salisbury nerve agent attack which killed one UK citizen and the suspects must be brought to justice. "Russia does not allow the extradition of its nationals, but European arrest warrants are out for those two individuals and if they set foot outside Russia we will be making every effort that they are brought to justice," she told the BBC ahead of Friday's meeting. Russia, China and India firmly oppose protectionism, unilateral actions and unlawful sanctions, Russian President Vladimir Putin said after a meeting of the BRICS grouping of emerging economies on the sidelines of the G20 summit. Three countries agree on the need to rely on international law, respect national sovereignty and refrain from interference in internal affairs of other nations, Mr Putin said after talks with Chinese President Xi Jinping and Indian Prime Minister Narendra Modi. He added that they have held meetings of foreign ministers and top security officials to co-ordinate action against terrorism, drug trafficking and other challenges. The BRICS grouping also includes Brazil and South Africa. UN Secretary-General Antonio Guterres is appealing for a de-escalation of tensions in the Arabian Gulf and the preservation of the 2015 nuclear deal with Iran. He told reporters on the sidelines of the G20 summit in Japan on Friday that the deal was a factor of stability and that "it will be very important to preserve it". He says avoiding a confrontation in the Gulf was a major concern for key players attending the G20. US President Donald Trump is to discuss Iran with other world leaders. He pulled the US out of the deal last year and imposed crippling sanctions on Iran. Earlier Mr Trump said there was “absolutely no time pressure” in dealing with Iran as European nations pushed to salvage what remains of the accord and avert a slide toward war. Donald Trump jokingly told Vladimir Putin not to interfere in the upcoming US election as the American and Russian leaders met in Osaka. Both leaders have disputed the finding of US intelligence official that Russia attempted to influence the 2016 election that put Mr Trump in office. During brief opening remarks before their meeting in Osaka, Mr Trump was asked whether he would warn Mr Putin against future election meddling. “Of course I will,” he replied. “Don’t meddle in the election, president,” Mr Trump then told Putin, pointing his finger at his Russian counterpart. “Don’t meddle in the election,” he repeated. Mr Putin smiled and turned to his translator. After she told him what Trump had said, he laughed. Mr Trump looked at Mr Putin, shook his head and smiled. Mr Trump has repeatedly disputed the consensus of US intelligence officials that the Kremlin interfered in the 2016 election, and has often chided reporters who ask whether he’ll warn Mr Putin against further meddling in the 2020 presidential election. Earlier on Friday, Donald Trump had meetings with German Chancellor Angela Merkel, Indian Prime Minister Narendra Modi and Japanese Prime Minister Shinzo Abe. He described Ms Merkel as a "fantastic person" said they "have many things to talk about" but did not say whether he would bring up his earlier complaint that Germany was taking advantage of US support in Nato. Ms Merkel said she wanted to discuss the crisis with Iran, counterterrorism and West Africa, where Germany is helping local governments to counter a surge in extremist militancy. Mr Trump's meeting with Indian Prime Minister Narendra Modi, who first joined the US and Japanese leaders at breakfast, came months after Mr Modi's re-election and amid strained ties with India over trade tariffs. "I think we’re going to have some very big things to announce,” Mr Trump said on India. “Very big trade deal.” India recently raised duties on nearly 30 American imports in retaliation for Mr Trump's increased tariffs on Indian metal exports last year and the scrapping of trade privileges this month. However, the US president said in Osaka that he and Mr Modi had become "great friends" and their countries "have never been closer". Speaking through a translator, Mr Modi said he wanted to focus on four issues: Iran, 5G communications networks, bilateral relations and defence relations. On Japan, the US president said he will be announcing some very big trade transactions with Tokyo without elaborating. European Union President Donald Tusk has blasted a comment by the Russian president that liberalism is obsolete. Mr Tusk said on Friday that such comments suggest a belief that "freedoms are obsolete, that the rule of law is obsolete and that human rights are obsolete." Mr Putin said in an interview with the <em>Financial Times</em> that "the liberal idea has become obsolete. It has come into conflict with the interests of the overwhelming majority of the population." Both leaders are attending the G20 the summit. In a press statement, Mr Tusk said: "We are here as Europeans also to firmly and unequivocally defend and promote liberal democracy. "What I find really obsolete are: authoritarianism, personality cults, the rule of oligarchs. Even if sometimes they may seem effective." In his interview, Mr Putin also praised the US president for trying to stop the flow of migrants across the from Mexico, saying that liberalism "presupposes that nothing needs to be done. That migrants can kill, plunder and rape with impunity because their rights as migrants have to be protected."