Some 900 people have fled the Iraqi city of Mosul and crossed the border into Syria, the UN refugee agency says.

This is the first large group of civilians confirmed to have escaped since the Iraqi government began its offensive to liberate Mosul from the so-called Islamic State (IS) on Monday.

As many as 1.5 million are thought to be in Mosul, with up to 5,000 fighters.

There are fears the militants will use the civilians as human shields as Iraqi forces get closer to Mosul.