Contrary to usual military doctrine, the leaders of the UN-mandated International Security Assistance Force (ISAF) in Afghanistan have announced their assault well in advance in a bid to warn the Afghan population.

Operations will be challenging and we should expect Afghan and NATO and ISAF casualties, James Appathurai told journalists in Brussels.

The aims of this operation are very clear and there is no reason to hide them ... The aim of the operation is also to make a point that the Afghan government can establish its authority whenever and wherever it wants, he said.

The assault, codenamed Moshtareq (Together), is the first major operation under ISAFs new doctrine, which is aimed at backing up military power with a strong civilian follow-through.

The government of Afghanistan has made preparations to provide immediate support and help to civilians affected by the operation as well as assistance for long-term development, Appathurai said.

The success of this operation will not be in the military phase, it will be in the weeks and months to come, as the people of central Helmand feel the benefits of security, better governance, justice and economic opportunities, he said.

The idea of announcing the assault in advance has split commentators, with some seeing it as an open invitation to the Taliban to leave the area - or to set up extra defences.

Civilians needed to be warned ... There has been no ultimatum to the Taliban. They can put down their guns, they can leave or they can fight, Appathurai said.