AWS CLI authentication

I have installed aws cli on my cygwin, created a IAM user, downloaded its access key information.

in the ~/.aws/credentials contain

[default]
aws_access_key_id = xxxxxxxxxxxxxxxxx
aws_secret_access_key = xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

and ~/.aws/config contain

[default]
region = us-east-1
output = text

But I get authentication error:

$ aws ec2 describe-regions
A client error (AuthFailure) occurred when calling the DescribeRegions operation: AWS was not able to validate the provided access credentials

Any idea where I am going wrong?