Switzerland today accused the US government of conducting a heavy-handed "fishing expedition" in its demands for the names of 52,000 Americans using Swiss bank accounts.

The powerful Internal Revenue Service is demanding UBS hands over the identities of American citizens it suspects of tax evasion.

The issue has caused outrage in Switzerland, where the banking community feels it is the subject of a witch hunt by an overbearing superpower.

A Swiss government filing in Miami today said if the American court were to press ahead in forcing UBS to act in contravention to Swiss secrecy laws, it would "violate Swiss sovereignty and international law". It branded the US summons an overly broad "fishing expedition" type of request, clearly inconsistent with recent treaties.

UBS made a similar filing hours earlier, stating that if it were to comply with the IRS request, the bank would be in breach of Swiss laws. With leaders in other recession-hit countries, Barack Obama has made great political currency from attacking tax havens.