How do I open or smash these silver blocks and padlocks?

Having reached the end of the game's storyline, we're now freeplaying around Middle Earth, picking up collectables, etc. The silver blocks and padlocks (as modelled below by Frodo) are getting in the way, as we don't seem to have a character available that can deal with them (or, we do and I've failed to notice).

Presumably, there is a character and/or a craftable tool that can do the job.
So which characters or tools can I use to break silver objects, and how do I obtain them?

Solution 1:

In order of first available in terms of game process, the following can be used to destroy these blocks:

Berserker Orc character

Purchased at a cost of 200000 studs.

Becomes available after completing the story level Helm's Deep

The character can be found on the world map, near Helm's Deep.
You can find him behind the Deeping Wall.

Mithril Fireworks item

Forged with a cost of 16 Mithril blocks.

Plan becomes available after the storyline level The Black Gate.

The plan can be found on the world map, near Barad-dúr (Sauron's Tower).
It's located above the door of the gate on the east side.