Matthew Csák laid siege Buda in June 1311, and Ladislaus Kán declined to assist the king. Charles sent an army to invade Matthew Csák's domains in September, but it achieved nothing. In the same year, Ugrin Csák died, enabling Charles to take possession of the deceased lord's domains, which were situated between Požega in Slavonia and Temesvár (present-day Timișoara in Romania). The burghers of Kassa (now Košice in Slovakia) assassinated Amadeus Aba in September 1311. Charles's envoys arbitrated an agreement between Aba's sons and the town, which also prescribed that the Abas withdraw from two counties and allow the noblemen inhabiting their domains to freely join Charles. However, the Abas soon entered into an alliance with Matthew Csák against the king. The united forces of the Abas and Matthew Csák besieged Kassa, but Charles routed them in the Battle of Rozgony (now Rozhanovce in Slovakia) on 15 June 1312. Almost half of the noblemen who had served Amadeus Aba fought on Charles's side in the battle. In July, Charles captured the Abas' many fortresses in Abaúj, Torna and Sáros counties, including Füzér, Regéc, and Munkács (now Mukacheve in Ukraine). Thereafter he waged war against Matthew Csák, capturing Nagyszombat (now Trnava in Slovakia) in 1313 and Visegrád in 1315, but was unable to win a decisive victory.