Unable to copy from S3 to Ec2 instance

I am trying to copy a file from S3 to an Ec2 instance, here is the strange behaviorFollowing command runs perfectly fine and show me the contents of s3, that I want to access

$aws s3 ls2016-05-05 07:40:57 folder12016-05-07 15:04:42 my-folder

then I issue following command (also successful)

$ aws s3 ls s3://my-folder2016-05-07 16:44:50       6007 myfile.txt

but when I try to copy this file, I recive an error as follows

$aws s3 cp s3://my-folder/myfile.txt ./

A region must be specified --region or specifying the region in a configuration file or as an environment variable. Alternately, an endpoint can be specified with --endpoint-url

I simply want to copy txt file from s3 to ec2 instance.At least modify the above command to copy the contents. I am not sure about region as If I visit S3 from web it says

"S3 does not require region selection"

What is happening on the earth?