Europe has weeks to save the euro and must create an "immediate" rescue plan, the United States and Britain plan to tell Germany Thursday, UPI cited Britain as saying. Such a rescue plan could involve Germany pledging to underwrite struggling countries' debt, officials said. British Prime Minister David Cameron was to tell German Chancellor Angela Merkel in Berlin Thursday he and U.S. President Barack Obama believe an authoritative agreement that fully gets the job done must be reached this month -- and there are two crucial summits in which to do it, officials said. Those meetings are the Group of 20 summit in Los Cabos, Mexico, June 18-19 -- when Obama, Cameron, Merkel and other leaders of 19 major-economy countries and the European Union get together -- and an EU leaders summit in Brussels June 28-29. The G20 summit will take place a day after Greek elections that could push Greece closer to dropping out of the eurozone if voters choose a government that repudiates Greece's debts or is unwilling to accept international lenders' further austerity measures to qualify for more aid, analysts say. Downing Street said Cameron and Obama agreed in a phone call Tuesday on the critical need for direct action. "They agreed on the need for an immediate plan to tackle the crisis and to restore market confidence as well as a longer-term strategy to ensure a strong single currency," a Cameron spokeswoman said Wednesday. Cameron has caused some irritation in Berlin and Paris by appearing to lecture eurozone leaders on actions he says they need to take to save the single currency, the British newspaper The Guardian reported. Britain is an EU member but is not part of the 17-country eurozone and does not use the euro as its currency. White House spokesman Jay Carney said Wednesday: "Our view is the Europeans have the capacity to act. They have taken some important steps, but more needs to be done." French Finance Minister Pierre Moscovici said the eurozone was ready to "mobilize very rapidly." European Central Bank President Mario Draghi said, "We stand ready to act," although his bank left interest rates steady at 1 percent Wednesday. Some market analysts had said they thought the eurozone central bank would lower the interest rate to make money easier to come by. "Some of these problems in the euro area have nothing to do with monetary policy ... and I don't think it would be right for monetary policy to fill other institutions' lack of action," Draghi said in explaining why the bank left the rate unchanged.