[Python] Not a valid OPENSSH private key file - Paramiko

I'm trying to connect to a host using paramiko. I'm able to successfully connect to the host through winscp using the private key, but the script fails with below error

raise SSHException("not a valid {} private key file".format(tag)) paramiko.ssh_exception.SSHException: not a valid OPENSSH private key file

import paramiko
ssh = paramiko.SSHClient()

ssh.set_missing_host_key_policy(paramiko.AutoAddPolicy())

ssh.connect('hostname.com', username='user', key_filename='private.ppk')

stdin, stdout, stderr = ssh.exec_command('ls')
print(stdout.readlines())
ssh.close()

Any suggestion would be appretiated,

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