Six Western troops, including three Americans, were killed Monday in Afghanistan, underscoring warnings that casualties will increase as more foreign troops stream into the country and step up efforts against the Taliban.

Despite the rise in violence, support among Afghans for the presence of foreign forces has increased. A poll released Monday found that nearly seven in 10 Afghans support the presence of U.S. forces in their country, and 61 percent favor the military buildup. However, it said support for U.S. and NATO forces drops sharply in the south and east where the fighting is the most intense.

Monday was the deadliest day for the NATO-led international force in more than two months.

The Americans died in a firefight with militants during an "operational patrol" in southern Afghanistan, U.S. military spokesman Col. Wayne Shanks said. He declined to provide on the exact location of the clash or their branch of service pending notification of family members.

The deaths raised to at least 10 the number of U.S. service members killed in Afghanistan so far this year, according to an Associated Press tally.

A French officer was killed during a joint patrol with Afghan troops in Alasay, a valley largely under insurgent control that NATO is trying to reclaim. Another French service member was seriously wounded in the attack some 50 miles (80 kilometers) northeast of Kabul. Eight French troops were in the patrol, said spokesman Col. Jacky Fouquereau.

NATO said another service member was killed in the clash but did not release the nationality. It said a sixth service member was killed by a roadside bomb in the south.

French President Nicolas Sarkozy, whose country has lost 37 troops in Afghanistan since 2001, condemned what he called "blind violence" and expressed his determination to keep forces in the country.

The previous deadliest day was Oct. 27 when eight U.S. troops were killed. Seven CIA agents and a Jordanian intelligence officer also were killed by a suicide bomber on Dec. 30.

Officials said earlier Monday that bombs killed another American service member and two Afghan road construction workers in separate attacks Sunday in southern Afghanistan. A district mayor also was killed in an ambush by gunmen inside a bazaar in the Dil Aram district of the southern Nimroz province, according to the Interior Ministry.

The southern half of the country, the Taliban heartland, has frequently been hit by attacks as the U.S. military builds up its presence in the area. Most of the 30,000 additional American troops that President Barack Obama has ordered to Afghanistan will be deployed there.

U.S. military officials have acknowledged that the insurgency has the momentum and warned that the troop buildup ordered by President Barack Obama is likely to lead to more casualties as the fight intensifies.

The top U.S. commander in Afghanistan, Gen. Stanley McChrystal, said he believes the troop surge in Afghanistan is turning the tide against the Taliban.

He cited as evidence of progress a meeting he recently held in a river valley in Helmand province, an area where the Taliban has been strong and one of the first targets of the surge.

"When I sit in an area that the Taliban controlled only seven months ago and now you meet with a shura of elders" — a traditional meeting — "and they describe with considerable optimism the future, you sense the tide is turning," he said during an interview aired Monday on ABC television.

The poll of a national random sample of 1,534 Afghan adults was conducted from Dec. 11 to Dec. 23 by ABC News, the BBC and ARD German TV, their fifth since 2005. It found support for U.S. forces had risen to 68 percent from 63 percent in 2009.

The poll has an error margin of plus or minus 3 percentage points. Field work was done by the Afghan Center for Socio-Economic and Opinion Research in Kabul, a subsidiary of D3 Systems Inc. in Vienna, Va.

Nationwide, 10 percent of Afghans support the Taliban, but the insurgents are backed by a higher percent of the population — 27 percent — in the country's southwest, it said.

On Sunday, a British correspondent and a U.S. Marine were killed by a roadside bomb in that region.

Sunday Mirror journalist Rupert Hamer, 39, was the first British journalist killed in the conflict.

Hamer and photographer Philip Coburn, 43, were accompanying a U.S. Marine patrol Saturday when their vehicle was hit by a makeshift bomb near the village of Nawa, the British Defense Ministry said. Coburn was seriously wounded.

Afghan President Hamid Karzai on Monday expressed condolences to Hamer's family as well as to the British media. Karzai said he appreciated the "brave journalists" who risk their lives in Helmand.

NATO troops operating in Helmand province also confiscated and destroyed a ton of opium found in the back of a vehicle during a patrol, the alliance said in a statement. It said the driver and two passengers were detained after they tried to flee.

Finding ways to steer farmers away from growing opium poppy and other agricultural reforms is on the agenda of visiting Agriculture Secretary Tom Vilsack, who arrived Sunday.

The Obama administration sees agriculture as the primary non-security element in lifting Afghanistan out of poverty and fighting extremism.