FileZilla works, SFTP not

I need to connect to an sftp-site with a private/public key combination. I've sent my public key to the site administrator and can connect with FileZilla without any problems. Within FileZilla I specified the location of my private key in the SFTP-settings. I would like to automate my FTP commands in a script, so my next step was to try sftp. I tried sftp with the -i option referring tot the private key file. I've also tried to copy the private key file to the .ssh-directory and chmod the key file to 600. But each time sftp requires a password after connecting, whereas FileZilla works out-of-the-box. Can you help me to solve this so I can consider scripting my downloads? Tx for your help Ivan

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