The ability for the whole of the international mathematics community to participate in the ICM in a safe and open atmosphere of collegiality and friendship is paramount. 
The recent military escalation in Ukraine makes this impossible, and AustMS can no longer support the hosting of the congress in St Petersburg.

The Executive Committee of the IMU has decided on 26/02 to run the ICM as a fully virtual event, with the General Assembly to be held prior to the event at a yet-to-be-determined location. For the full statement on the ICM by the IMU, see here.

On 27 Feb. this response was further qualified as follows.

The Executive Committee of the IMU wants to state the following: 
1. The IMU General Assembly and the ICM will be conducted without any financial contribution from the Russian Government.
2. No official or representative of the Russian Government will be part of the organization or activities of the ICM.
3. All mathematicians are welcome to participate in the activities of the ICM.
4. ICM satellite conferences are and have always been outside the purview of the IMU.