Moving by land and through the air, the foreign troops are seeking to destroy the Taliban's largest haven in a bid to reassert the dominance of the Afghan government across a large arc of southern Afghanistan, reports the New York Times.
The force of about 6,000 Marines and soldiers, a majority of them Afghan, began moving into the city and environs before dawn. As Marines and soldiers marched into the area, several hundred more swooped out of the sky in helicopters into Marja itself.
Marines from Company K, Third Battalion, Sixth Marines, landed near an intersection of two main roads at the northern fringes of Marja, piled out of the their helicopters and scattered into the houses and compounds around them.
In the quiet dark of 2:40 am, Company K met no resistance. But none of the Marines believed the peace would last the night.
"Basically, we are going into a main hornets' nest," the paper quoted Captain Joshua P Biggers, Company K's commander, as saying.
Just after midnight, aircraft bombed the southernmost portion of Marja, where officials believed foreign fighters were hiding.
Later, Marines and Afghan soldiers began setting up cordons to the northeast, south and west of the city, in anticipation of a ground assault that was expected to begin within hours.
The operation, dubbed Moshtrarak, which means 'together' in Dari, is the largest offensive military operation since the American-led coalition invaded the country in 2001.
Its aim to flush the Taliban out of an area -- about 75 square miles -- where insurgents have been staging attacks, building bombs and processing the opium that pays for their war.
The invasion of Marja is being touted as a crucial part of a larger campaign to secure a 200-mile arc that would bisect the major cities in Helmand and Kandahar Provinces, where the Taliban are the strongest.
That campaign, which is expected to last months, is designed to reverse the Taliban's momentum, which has accelerated over the past several years. The American, Afghan and British troops began moving into Marja before first light, making their way through a broad, flat area crisscrossed by irrigation canals and scattered with opium factories as well as, in all likelihood, several hundred hidden bombs.
The troops that came in by air carried portable footbridges and mine detectors. The troops moving in on armored personnel carriers were being led by enormous fortified vehicles designed to clear road of bombs.
American and Afghan commanders said they expected the heavy fighting to be over in a number of days. The commanders say the overriding purpose of the campaign will take shape, when they bring in a fully formed Afghan government and security force that can hold the city so that the Taliban cannot return.
Several hundred Taliban fighters are believed to be inside the city as well, which could make for a close and bloody fight. Despite that, the North Atlantic Treaty Organisation and Afghan attackers appear to enjoy a huge numerical advantage -- possibly more than 10 to 1.
The assault came as a surprise to no one. American commanders and Afghan officials have said publicly for weeks that an invasion of Marja was imminent, in an effort to chase away as many Taliban fighters as possible and keep the fighting, and civilian casualties, to a minimum.
The hope is to win the support of local residents, even at the expense of letting Taliban get away. The centerpiece of the Marja operation is the Afghan government-in-waiting that will move into the town the moment the shooting stops.
That is an attempt to compensate for past failures, when an inadequate government was left behind.
Image: A NATO commander keeps a firm grasp of his search dog before being mobilised for Operation Moshtarak at Camp Bastion, on Friday
Photograph: Handout / Reuters