Jenkins access private BitBucket repo over SSH

I'm having trouble getting Jenkins to clone a git repository on BitBucket via SSH. It's failing with the following message:

Building in workspace /var/lib/jenkins/workspace/test
[ssh-agent] Using credentials git (git@bitbucket.org:<user>/<repo>.git)
[ssh-agent] Looking for ssh-agent implementation...
[ssh-agent]   Java/JNR ssh-agent
[ssh-agent] Started.
Checkout:test / /var/lib/jenkins/workspace/test - hudson.remoting.LocalChannel@2b619bca
Using strategy: Default
Fetching changes from 1 remote Git repository
Fetching upstream changes from origin
ERROR: Problem fetching from origin / origin - could be unavailable. Continuing anyway
hudson.plugins.git.GitException: Command "git fetch -t origin +refs/heads/*:refs/remotes/origin/*" returned status code 128:
stdout: 
stderr: ssh: connect to host bitbucket.org port 22: Connection refused
fatal: The remote end hung up unexpectedly

Steps taken

Create an SSH keypair
Add the public key as a deployment key for the repository on BitBucket
Install the SSH key and username (have tried both 'git' and my BB account name) in the Jenkins Credentials manager plugin
Attempt to clone the repository in the build using a URL in form of

git@bitbucket.org:<user>/<repo>.git

I've also tried not using the credentials manager and manually installing the keys in /var/log/jenkins/.ssh/, but to no avail.

Any ideas what I'm doing wrong?

As @user1562655 suggested out, the clone was failing due to another issue -- in this case the firewall was blocking outgoing ssh on port 22.

The fix was to use port 443 (as the server allows this), and a different BitBucket URL:

ssh://git@altssh.bitbucket.org:443/<user>/<repo>.git

…instead of

ssh://git@bitbucket.org:<user>/<repo>.git

More info on the scheme is available here:

UsetheSSHprotocolwithBitbucket-SSHonPort443