WASHINGTON: Average long-term US mortgage rates fell sharply this week amid concern over a labour market that has shown recent signs of weakness. Mortgage giant Freddie Mac said on Thursday the average rate on a 30-year fixed-rate mortgage dropped to 3.76 per cent from 3.85 per cent a week earlier. The rate on 15-year fixed-rate mortgages declined to 2.99 per cent from 3.07 per cent.