Helmand is the most troubled region in Afghanistan with the highest level of activity by insurgents, mostly remnants of the Taliban ousted from the government by US-led forces in late 2001.
The current operation, called Moshtarak (Dari for "together"), is aimed at driving the Taliban from their strongholds and is part of Washington's new war strategy for Afghanistan announced late last year.
The town of Marjah continues to see sporadic resistance.
Over a dozen foreign soldiers and at least two of their Afghan counterparts have been killed during Moshtarak. Dozens of Taliban fighters have also died although the authorities have yet to give a precise figure.
At least 15 civilians have also been killed in the offensive, 12 of them by a rocket fired by US forces and intended to hit Taliban resistance.
Operations are set to expand to other Taliban strongholds, particularly in the neighbouring province of Kandahar, where the Taliban maintain a large presence.
About 121,000 international troops, mainly from the United States and NATO, are stationed in Afghanistan fighting the Taliban.