Is there a limit by government regulations on large amount transfer from international account to U.S. account. Same person on both accounts. Or is limit set by bank?
There is no legal limit, and banks can handle 9 digit amounts.
Note that if the money appears from thin air, the IRS might appear and want it treated as taxable income, potentially with fees and interest for previous years. If the money/asset was already yours before, it will be on your previous tax returns somewhere, be it as ‘foreign assets’ or ‘gift’ or whatever (unless you committed ‘tax fraud’ by not listing it).