Zrinyi reported to Emperor Leopold I on the situation in Kanitzsa and the siege was scheduled for April 8, but due to the German troops' procrastination, it did not begin until the end of the month.

The siege was not initially successful due to a lack of gunpowder and cannons, so it was decided to dig trenches all day and night.

[2] On April 30, the cannons began bombing the castle, however, they could not make a breach in the walls suitable for an attack despite the one-month artillery fire.

After several days of work, military engineer Wassenhoff managed to restore the embankments, during which time the bombardment of the castle was paused.

[citation needed] Yet the siege should have been hurried, for the Ottoman army of Grand Vizier Köprülü Fazil Ahmed Pasha was approaching.

Zrínyi sent an assistant officer called Renaut to Wolfgang Julius von Hohenlohe with the news under the cover of night, but a team of defenders breaking out of the castle captured the envoy.

Zrínyi was reasoning to carry on with the fight and confront the oncoming enemy, but the imperial leaders feared they could fall between two fires if the defenders also sallied out of the castle.

Montecuccoli retreated as far as Vas County and decided to engage in a decisive battle there with the Grand Vizier's troops, which were outnumbered by several five times.