Originally posted by the Voice of America. Voice of America content is produced by the Voice of America, a United States federal government-sponsored entity, and is in the public domain. World Leaders Gather in Canada for G8, G20 Summits Dan Robinson 25 June 2010 Britain's Prime Minister David Cameron, left, is greeted by Canadian officials as he arrives for G-20 Summit in Toronto, Canada, 24 June 2010 Photo: AP Britain's Prime Minister David Cameron, left, is greeted by Canadian officials as he arrives for G-8, G-20 Summit in Toronto, Canada, 24 June 2010 World leaders are gathering in Canada for two summits of major industrialized nations, and the world's leading developing nations. Presidents and prime ministers began arriving in Toronto Thursday for the G8 and G20 summits, including Russian President Dmitri Medvedev, Japanese Prime Minister Naoto Kan and British Prime Minister David Cameron. In an opinion piece in the Globe and Mail newspaper, the British leader said the summits need to be more than "just grand talking shops" and make progress on key priorities like the global economy. Officials say leaders will discuss security concerns but that a significant focus of the talks will be on ways to ensure sustained economic growth while battling growing budget deficits. U.S. President Barack Obama is expected to arrive in Canada Friday for talks with G8 leaders in Muskoka, north of Toronto. On Saturday, the focus switches to Toronto and talks of the larger G20 nations, which account for 90 percent of the global economic output and 80 percent of world trade. On Thursday Mr. Obama called on countries to "re-balance" to allow their economies to prosper. Friday's meetings of the G8 will also include a session with key African leaders on development and maternal and child health issues. The G8 summit is also expect to discuss peace and security issues, with a focus on Iran, North Korea, Afghanistan, Pakistan and the Middle East peace process. In a message ahead of the summits, Canadian Prime Minister Stephen Harper urged world leaders to take action on some of the world's most pressing problems. Canadian authorities have arrested at least three people in connection with possible threats of violence in recent days. Canada has spent close to $1 billion on security. An unusually large number of officers can be seen on streets in Toronto, and many are equipped with bullet-resistant vests, helmets and gas masks. Some information for this report was provided by AP, AFP and Reuters. .