Prince Eugene was made commander in chief of the Army in the newly conquered Pannonian Plain on 5 July 1697. His army consisted  of 70,000 men at full strength of whom only 35,000 were ready for battle. As the war chest was empty, Eugene had to borrow money in order to pay wages and to create a working medical service. The Habsburg Army consisted of German, Austrian, and Hungarian infantry and cavalry forces . Thanks to Palatine Paul Eszterházy, the Habsburg Kingdom of Hungary contributed to Ottoman-Habsburg wars with 20,000 soldiers. Serb light cavalry and Serbian Militia conscripts also took part in the coalition. When news arrived that the Sultan and his army were in Belgrade, Eugene decided to concentrate all his available troops from Upper Hungary and Transylvania and started to move his troops towards Petrovaradin. After the concentration took place, Eugene had an Imperial army of 50,000 to 55,000 men to face the Ottomans. On 18 July, in the village of Kolut, Eugene held a military review of his forces. Soon he left with forces to Petrovaradin via Sombor. During August, Eugene offered battle in the neighborhood of the fortress of Petrovaradin but the Ottomans, attempting to start a siege, refused to engage in battle. In September the Ottomans moved north in an attempt to capture the fortress of Szeged and the Imperial army followed. There were few Kuruc cavalries in the Ottoman army under Imre Thököly, however most of them fought alongside the Austrians. Thököly was in charge of the Ottoman cavalry in battle.
Question: What news caused Eugene to decide to concentrate his troops from Hungary and Transylvania and move them toward Petrovaradin?
Answer: Sultan and his army were in Belgrade