From the 9th century, the Pecheneg nomads began an uneasy relationship with Kievan Rus′. For over two centuries they launched sporadic raids into the lands of Rus′, which sometimes escalated into full-scale wars (such as the 920 war on the Pechenegs by Igor of Kiev reported in the Primary Chronicle), but there were also temporary military alliances (e.g. the 943 Byzantine campaign by Igor). In 968, the Pechenegs attacked and besieged the city of Kiev. Some speculation exists that the Pechenegs drove off the Tivertsi and the Ulichs to the regions of the upper Dniester river in Bukovina. The Byzantine Empire was known to support the Pechenegs in their military campaigns against the Eastern Slavic states.[citation needed]