But this is more a word of caution than a prohibition.

A word of caution: he may not answer you straight away.

But before you go, there are several words of caution.

But even at the time there were words of caution from those involved in the project.

Before you go, though, there are several words of caution.

But while members were supportive, several offered words of caution.

A little word of caution here, if you don't mind.

Then, in a changed tone, he spoke words of caution.

Then, with one last word of caution, we started on our climb.

But before you leave, two words of caution: Drive carefully.