China stepped up its campaign to combat rising inflation and damp the sizzling pace of economic growth Tuesday by further restricting lending at the nations banks after government data showed inflation remained persistently high in May. The central bank increased the so-called reserve requirement ratio, which dictates the amount of cash that banks must set aside, by 0.50 percentage point, effectively reducing the amount they can lend. The ratio has been raised six times this year alone and now stands at 21.5 percent for the biggest lenders. The latest increase came only hours after the national statistics bureau reported that consumer prices in China rose 5.5 percent last month from the same period a year earlier. That was slightly more than analysts had expected, and faster than the 5.3 percent increase in April. Soaring commodities prices, strong economic growth, wage pressures, and, in some cases, adverse weather conditions, have put the heat on inflation in many parts of the world.