'331 Password required.' connecting to DSL router

[Frédéric L. W. Meunier]

Hi. I don't know what's wrong with LFTP (4.0.6) or me, but it 
doesn't connect to my DSL router (SpeedTouch 510v6), which 
has no password. 'ftp' works fine.

lftp u...@192.168.1.254:~> open -u user
192.168.1.254
Password:
lftp u...@192.168.1.254:~> ls
---- Connecting to 192.168.1.254 (192.168.1.254) port 21
<--- 220 Inactivity timer = 120 seconds. Use 'site idle <secs>' to change.
---> FEAT
<--- 331  Password required.
---> AUTH TLS
**** Peer closed connection
---- Closing control socket
Interrupt

Using 'debug 9' returns the same lines.