Gold prices edged higher on Thursday on concerns about the eurozone debt crisis ahead of Spain's bond auction and a European Central Bank meeting, as robust buying from China and India also supported sentiment. Spot gold inched up 0.2 percent to $1,644.69 an ounce by 0704 GMT, holding steady above the key 200-day moving average at about $1,636. US gold gained 0.4 percent to $1,646.50.