If you didn't intent to leave your current job, or new opportunity looks flying sexy, it is a waste of time of everyone to attend the interview.

If you want to decline the interview, you can say,

"Well, i was looking for a job and might have been interested in the profile like this, but I have just taken up another assignment so I might not be willing change very soon."

I think this (just-joined-somewhere) is enough, for recruiter not to bother you.

If you didn't intend to leave your current job, or the new opportunity looks flying sexy, it is a waste of time of everyone to attend the interview.

If you want to decline the interview, you can say,

"Well, I was looking for a job and might have been interested in a position like this, but I have just taken up another assignment so I'm not be willing change very soon."

I think this (just-joined-somewhere) is enough, for recruiter not to bother you.