FtpWebRequest: URI prefix not recognized (with sftp)

I am trying to upload a file to an FTP server. FTP server address sftp://xxx.xx.xx.xx:xx

. When I try to do with it FtpWebRequest

. He throws out NotSupportedException

which reads:

The URI prefix is ​​not recognized.

code:

FtpWebRequest request = (FtpWebRequest)WebRequest.Create("sftp://xxx.xx.xx.xx:xx");