"Owing to" vs "because of"

Is it right that “Owing to” is always used in the beggining of a sentence, where it means ,’ because of’.
can’t we use it in the centre of a sentence?

Can any one tell me about the source of Free Collocations Dictionary , I want to download it.Because it is difficult to find a book in my city.

It is found in other parts of the sentence:

There’s no indication at all that is the end of their contribution. There is, in fact, all kinds of reason to believe that they will be there, but they can’t be there with troops owing to a constitution that the United States imposed upon them.

If we are about to enter a recession, it will be in large part owing to regulatory overreaction to criticism of the laissez-faire forces symbolized by Michael Milken. # Mr. Milken built his career on a simple observation.

The first such raid was against Mannheim on December 16th, 1940, but again was relatively ineffective owing to so many of the crews bombing wide.