Transfer a file from a remote to another one

[Ahmad Modaghegh <aiispassw@xxxxxxxxx>]

As mentioned in documentation (tuts), by using SCP and SFTP, It is 
possible to transfer a set of *LOCAL* file (or directories) through a 
secure SSH connection. But is it possible to transfer Files located on a 
public remote to another one?

Let's say there is host (serving sshd): x.x.x.x:22 and there is another 
one: y.y.y.y:22 (both on different machines). Now is it possible to 
transfer a file from the first one to another one using lib APIs 
directly (by sending the command from a third-machine)? I'm sure it is 
possible natively on ssh (CLI) as below:

scp nick0@x.x.x.x:file nick1@y.y.y.y:newfile

Thanks in advance.