Russian President Vladimir Putin, French President Emmanuel Macron, Japanese Prime Minister Shinzo Abe and IMF Managing Director Christine Lagarde are among the participants of the forum.
Putin and Macron met in France previous year, just weeks after Macron's inauguration.
The three-day St. Petersburg International Economic Forum (SPIEF) continues on Friday, May 25 in Russia's second largest city.
Putin also said Russian Federation was ready for dialogue with the United States, but that a proposed summit with U.S. President Donald Trump was not working out for now and was beset by problems.
The European Union has initially sided with the U.S. on the anti-Russian sanctions but it has recently taken a step back. "This is unacceptable and it has to end", he said.
Tensions have escalated after US President Donald Trump withdrew from the Iran deal and reimposed sanctions on the country.
"That was not desirable", Macron said, adding that the embassy move played a part in sparking fatal clashes between Palestinian protesters and Israeli security forces.
Macron said that Trump had, de facto, lost an global argument over the Paris climate change agreement because the worldwide consensus in support of the accord had held, even though Trump had made a decision to exit the deal. The step also hurt European and other worldwide firms who had to cut off business ties with the sanctioned entities for fear of punitive action by Washington.
Putin easily won re-election in March, extending his tenure by six years to 24 - which would make him Moscow's longest-serving leader since Soviet dictator Josef Stalin. "Trade is growing", Putin said in comments carried by state news agency TASS.
Putin called these sanctions "a new edition of protectionism" and suggested the United States was out of bounds by imposing restrictions on Russian Federation.
Jeremy Corbyn has called for a united Ireland
He will also talk about the issues around Brexit, with the Irish border and customs arrangements now dividing the Government. They added that Mr Corbyn "respects the Belfast Agreement and the process".
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Other players rumored to be destined for Arsenal include; Sokratis Papastathopoulos, from Borussia Dortmund, and Saul Niguez. If they are rumored to buy an elite player, during the transfer window, they play well which increases the odds of winning.