While reading through this question another occurred to me. If a headline reads
British PM says no to inflatable cars.
Is British a noun or an adjective? Granted, there are other noun forms of British but how about French in
French PM says yes!
The example from the original question quoted
Yemen PM Escapes Assassination
Since the adjective for the people of Yemen is Yemeni, this is clearly a noun adjunct. However, in those cases where the noun and the adjective forms are the same (British, French, Greek, Italian etc.) as in the example above, are these adjectives or nouns? They can be taken as either.