[nightspirit]

It seems that most of the time people point verses 2:190-194 as example, but frankly, they only tell to "fight those who fight you" [1].

However, in practice apparently some leeway in definition of what constitutes an attack on believers and reasonable retribution is used to justify things going on in Syria and, recently, in Europe. Or maybe they just don't care that much. It's not like medieval Europe followed the Gospels to the letter. The whole discussion is pretty academic.

[1] http://www.islamicstudies.info/tafheem.php?sura=2&verse=189