[DeLeeuw]

I agree with you, but I would take Ukraine off the list, although they had a strong motive.

Ukraine's strategic cornerstone is international relations, without which they cannot win the war.

Ukraine would never risk upsetting Germany, the EU's biggest economy, with such a drastic operation.

[kspacewalk2]

Also, how would Ukraine pull off such a mission in a sea it has no access to?

[GolfPopper]

A boat, some underwater explosive charges, underwater ROVs, and a team to operate all the above seems likely to be well within Ukraine's capabilities.

The first underwater ROV I found via googling is $10K: https://www.deeptrekker.com/shop/products/dtg3#

It seems like something within the technical capabilities and resources of any functioning non-microstate.

[mopsi]

And risk getting cut off from further military and economic support from allies? Highly unlikely.

[croes]

How many people do you need to blast a pipeline?

Don't have to be in line with the government of a country.