German engineering and industrial giant Siemens said Tuesday that its earnings targets for the current year were \"very ambitious\" and it was becoming more difficult to achieve them. \"Our guidance is very ambitious,\" Siemens chief financial officer Joe Kaeser told the Wall Street Journal Deutschland in an interview. \"It certainly hasn\'t gotten easier to achieve our goals since we released them. The headwinds have become stronger,\" Kaeser said. His comments sparked a sell-off in Siemens shares on the Frankfurt stock exchange, where they were showing a loss of 2.3 percent at 74 euros in a generally firmer market. Siemens, already cautious about its business year that started on October 1 in view of the economic fallout from the eurozone debt crisis, forecasts a modest 3.0-5.0 percent increase in sales this year from the 73.5 billion euros ($94 billion) posted in the 12 months to September 2011. Bottom-line net earnings are projected to remain stable at around 6.0 billion euros. \"For now, we have to work hard to meet our full-year targets,\" Kaeser said. \"We already said in the summer that the overall economic situation will have an impact on the investment behaviour of our customers,\" he said. \"When our customers invest less, we get fewer new orders.\"