According to the Assyrian King List [/riao/kinglists/assyriankinglist/assyriankinglist/index.html#Ashurdan] (AKL), Ninurta-tukultī-Aššur, son of Aššur-dān I, was the eighty-fourth ruler of Ashur. For information about the length of his reign, see introduction to his brother Mutakkil-Nusku.
The AKL records the that Ninurta-tukultī-Aššur was driven into exile in Babylonia by his brother Mutakkil-Nusku. Before that, while Ninurta-tukultī-Aššur held authority over Assyria (possibly as regent), the statue of Marduk that Tukultī-Ninurta I had taken to Ashur was returned to Babylonia (Grayson 1975, 176: 12-13). That act presumably garnered him favor with the king of Babylon since that ruler wrote a few letters to the Assyrian king, possibly Mutakkil-Nusku, on his behalf while he was exile. The vindictive tone of these badly damaged pieces of royal correspondence suggests that the Babylonian king intended to install Ninurta-tukultī-Aššur as the king of Assyria (Grayson 1998-2001, 527). Those plans were never realised and Aššur-rēša-iši I became king when his father Mutakkil-Nusku died.
Poppy Tushingham & Jamie Novotny
Poppy Tushingham & Jamie Novotny, 'Ninurta-tukultī-Aššur', RIA 2: Inscriptions of Adad-nārārī I to Aššur-rēša-iši I, Th RIA Project, 2023 [http://oracc.org/ninurtatukultiashur/]