The British-led Operation Silicon is the latest attempt to extend the shaky control of President Hamid Karzai's government in Helmand province, officials said.
Military officials said the effort involved some 1,100 British troops, 600 U.S. soldiers and more from the Netherlands, Denmark, Estonia and Canada. More than 1,000 Afghan government troops also were taking part.
The troops were targeting Helmand's Sangin Valley, an area near Afghanistan's strategic ring road that has "for too long been under the semi-control of the Taliban," said Lt. Col. Stuart Carver, a British commander.
"It is all part of a longer-term plan to restore the whole of Helmand to government control," Carver said. "You have to do it a piece at a time."
Meanwhile, a suicide bomber on motorcycle blew himself up next to a convoy of a private U.S. security contractor on Monday in volatile Kandahar province, killing one Afghan employee and wounding three others, police said.
The attack happened in Zhari district on the main highway linking Kandahar and the western city of Herat, said Kandahar police chief Esmatullah Alizai. He said there were no civilians in the vicinity of the attack.
In western Afghanistan, U.S.-led coalition and Afghan forces battled with Taliban insurgents over three days, leaving at least 136 suspected militants dead, a coalition statement said Monday.
The clashes in Herat province were the deadliest reported in Afghanistan since January and sparked angry protests by hundreds of villagers Monday, chanting "Death to America!"
Acting on intelligence about Taliban activity in Herat's Zerkoh Valley, coalition and Afghan forces attacked the insurgents and called in an air strike, destroying seven Taliban positions and killing 87 fighters during a 14-hour engagement on Sunday, the statement said.
Another 49 Taliban were killed two days earlier by a combination of gunfire and an air strike, it said, adding that a U.S. soldier also was killed in the engagement.
The coalition statement said there were no reports of civilians wounded in the two battles. It was not immediately possible to confirm the casualty figures independently.
On Monday, hundreds gathered in front of the police station and government headquarters in Shindand district where Zerkoh Valley is located, said district police chief Gen. Gul Aqa.
Aqa confirmed that the attack had killed "a large number of people" but did not have figure for the number of dead. Contrary to coalition claims, Aqa said the Afghan police and army were not involved in the clashes.
"The Americans carried out an independent operation in the Zerkoh," he said, adding that protesters were demanding to know why Americans did not inform Afghan forces beforehand.
Recent weeks have seen an upsurge in violence in Afghanistan after a winter lull, with Taliban-led militants stepping up attacks, and coalition and NATO forces launching a series of offensives against around the country.
The clashes in Herat appear to be the deadliest in the once-stable west of the country since the ouster of the Taliban regime in late 2001. Most of the fighting has been concentrated in the volatile south and east.
The fighting is also the deadliest reported nationwide since January, when NATO said that about 150 suspected Taliban crossing from Pakistan were killed by an air strike and ground fire in eastern Paktika province.