Without backing up his claim, US President-elect Donald Trump is blaming Islamic terrorism for deadly violence in Turkey and Germany and vowing anew to eradicate their regional and global networks.

Authorities in both countries were still investigating when Trump issued a pair of statements condemning the incidents on Monday. The White House had already described the episode in central Berlin, in which a truck rammed into shoppers at a Christmas market, as an apparent terrorist attack.

Trump called the brazen shooting of Russia's ambassador to Turkey as he attended a photo exhibit "a violation of all rules of civilized order". He added that a "radical Islamic terrorist" had assassinated the diplomat, Andrei Karlov.