US banks increasingly tightened loan conditions on subprime and non-traditional mortgages in recent months and became more cautious about prime mortgages, syndicated loans and commercial real estate, according to a survey by the Federal Reserve.

The quarterly survey of senior loan officers showed that more than 30 per cent of banks had tightened standards on subprime mortgages by mid-July, while 14 per cent had tightened standards on prime residential loans.