KG26 and neutral shipping 1940

[Brian]

Hi guys

What were the 'rules of engagement' for KG26 in particular during attacks on merchant shipping in early 1940, when many neutral ships were at sea? For example, I have note that KG26 attacked and sank/damaged two Greek, one Norwegian and one Italian vessels in February 1940, and three Dutch, two Norwegian and one Italian in March 1940.

Were crews supposed to check identities of vessels in British or international waters at this time?

Any help will be appreciated.
Thanks

Cheers
Brian