Curl fails to connect via SFTP

Question

I am trying to set up curl to fetch a file from an SFTP server on my Fedora box. The command I am running is:

curl -s -S -u 'user:pass' -k 'sftp://aserver.com/afile' -o afile 2>&1

The error I am getting is:

afile: curl: (2) Failure initializing sftp session: Unable to send SSH_FXP_INIT

I can connect to the server using sftp with no errors.

Has anyone seen this before and has a workaround? Perhaps it's some curl parameter I am not setting?

Here's the output of curl -v

curl 7.20.1 (x86_64-redhat-linux-gnu) libcurl/7.20.1 NSS/3.12.8.0 zlib/1.2.3 libidn/1.16 libssh2/1.2.4
Protocols: dict file ftp ftps http https imap imaps ldap ldaps pop3 pop3s rtsp scp sftp smtp smtps telnet tftp
Features: AsynchDNS GSS-Negotiate IDN IPv6 Largefile NTLM SSL libz

Here's the trace from curl:

* About to connect() to aserver.com port 22 (#0)
*   Trying 123.123.132.123...   
% Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
Dload  Upload   Total   Spent    Left  Speed
  0     0    0     0    0     0      0      0 --:--:-- --:--:-- --:--:--     0 connected
* Connected to aserver.com (123.123.123.123) port 22 (#0)
* SSH authentication methods available: password,publickey,keyboard-interactive
* Using ssh public key file /home/user/.ssh/id_dsa.pub
* Using ssh private key file /home/user/.ssh/id_dsa
* SSH public key authentication failed: Unable to open public key file
* Initialized password authentication
* Authentication complete
* Failure initializing sftp session: Unable to send SSH_FXP_INIT
* Closing connection #0

curl: (2) Failure initializing sftp session: Unable to send SSH_FXP_INIT

Follow up: I gave up on curl after days of trying to get it to work. Ended up writing a fetching utility in Java using a third-party FTP/SFTP/FTPS library. Sad to say that this took me less time than I spent troubleshooting curl and the OS libraries.