WHERE is Marjah?

Marjah is a town in Nad-e-Ali district, in central Helmand Province, about 15 miles west of the provincial capital, Lashkar Gah.

It is surrounded by grids of irrigation canals, built with US aid money in the 1950s, that supply water to a lush green zone where huge amounts of opium are grown.

For years the area has been dominated by rival militias who vie for control of the lucrative drugs trade.

Why is Operation Moshtarak significant?

Marjah has an important strategic location at the heart of the populous central belt of Helmand, which is Afghanistan's most dangerous province.

Until now the area has been outside the control of the Afghan government and Nato forces, allowing the Taliban to establish a power base there.

Which forces will be involved?

Operation Moshtarak will be led by the US Marine Corps but British troops are also heavily involved.

Soldiers from the Grenadier Guards Battle Group, the Royal Welsh and the Scots Guards took part in preliminary operations.

Why has the operation been so well publicised in advance?

The hope is that civilians will leave their homes and many Taliban fighters will melt away before the operation begins. This would mean fewer casualties.