Ukraine

but as UA is currently on the offence

Thats certainly true on the south and east, but not so true on the north where they're either holding the borders with Russia or actively defending against an offensive near Kupiansk.

I think they concentrate more on clearing mine fields instead of planting them.

Well yes, but Ukraine can do both at once. The best evidence is this thread where there is a video of a robot laying mines that we're watching.