France, Jan. 19 -- After US President Donald Trump threatened to impose tariffs of up to 25 percent on a string of European countries unless Greenland is ceded to the United States, the European Union finds itself contemplating a powerful - and so far unused - weapon in its trade arsenal: the so-called "anti-coercion" instrument.

The warning from Trump was met with shock across Europe over the weekend. The US president said the tariffs would target EU members Denmark, Finland, France, Germany, the Netherlands and Sweden - as well as non-EU Britain and Norway- unless Denmark hands over Greenland, an autonomous territory within the Danish kingdom.

The remarks triggered alarm in European capitals and prompted leaders of the 27-nation bloc ...