I've encountered this sentence as an example on wiktionary:
In den letzten Tagen hat es wieder vermehrt Anschläge im Irak gegeben.
As far as I know
vermehrt is a partizip 2 form of
vermehren which is acting as a verb here. But how is it declined here? Shouldn't it be
vermehrte according to strong declination of adjectives (without article)?