Syrian and allied Russian forces are preparing for an assault on the last-remaining rebel stronghold of Idlib.

The United Nations has warned that an all-out offensive on the province, where as many as three million people are trapped, could lead to an unprecedented humanitarian crisis in the war-torn country.

They are hoping a last-minute summit between the major world powers that back opposing sides in the conflict can reach a political agreement that could at least limit the number of civilian casualties.

However, a barrage of Russian air strikes on Tuesday suggested they were in no mood for compromise. 

What is the situation in Idlib?

Idlib is a province in northwestern Syria and is now the…