Disable su and sudo access for users

Question

I have created a couple of users who use their SSH Keys to log in on a server.

I don't want any user to have root access, i.e, no user should be able to do sudo su or su - another user.

When I check the user, I can see only these

id user
uid=1001(user) gid=1001(user) groups=1001(user)

I have checked across the internet, I found how to disable sudo access for users with a password but I want to disable it for users who are using their SSH keys to log in?

I want to disable sudo and su access for user that log in using SSH. How will I do it?

Edit 01:

I have done the following;

sudo deluser user sudo

/usr/sbin/deluser: The user is not a member of group `sudo'.

and

sudo gpasswd -d user sudo

Removing the user from group sudo
gpasswd: the user is not a member of 'sudo'

After that, I checked

sudo -l -U user

User  may run the following commands on the server:
    (ALL) NOPASSWD: ALL

User is still able to run sudo su and get root access.

EDIT 02:

@Panki, The snippet

visudo

# User privilege specification
root    ALL=(ALL:ALL) ALL

# Members of the admin group may gain root privileges
%admin ALL=(ALL) ALL

# Allow members of group sudo to execute any command
%sudo   ALL=(ALL: ALL) ALL

Solution

You do not create a user using SSH keys. The user logs in to the machine using SSH keys after creation.

For sudo, there is no difference in how the user authenticates.

To prevent users from using sudo, remove them from the group sudo. To prevent them from using su, don't tell them the root password.

Comments

[Panki]

Well, you forgot to mention in your question that your /etc/sudoers file allows anybody without a password to run every command as root. This is a very bad idea for obvious reasons. You should edit the file (use visudo for this) and restore a sane state.

[Kamil Maciorowski]

(ALL) NOPASSWD: ALL comes from somewhere. If it's not directly in the sudoers file then maybe the file contains #include or #includedir (they are not comments). Learn what they do (see man 5 sudoers), locate files/directories they point to and investigate. If you need to change anything, use visudo -f.

[Siddarth Hegde]

Thanks, @Panki, I have also done the following which I have added in the edit. User access only using SSH, not password