The US death toll for August stood at 55 — three-quarters of them in the second half of the month as the Taleban fight back against US pressure in southern and eastern strongholds. American losses accounted for more than 70 percent of the 76 fatalities suffered by the entire NATO-led force.
NATO said four of the Americans were killed by a roadside bomb in eastern Afghanistan, while a fifth died in a gunfight with insurgents in the country's south. No other details were released.
Until the late month spike, it appeared that the death toll for August would be well below the back-to-back monthly records of 66 in July and 60 in June.
By the middle of August only 13 Americans had been killed — in part because of greater use of heavily armored vehicles and other defenses against roadside bombs, the Taleban weapon of choice.
The reason behind the sudden spike in deaths was unclear because few details about the casualties are released for security reasons.
Most of the US deaths occurred in the southern provinces of Helmand and Kandahar, longtime Taleban strongholds that are the focus of the American-led operation against the insurgents.
As the US formally ends its combat role in the Iraq war, NATO and Afghan forces are ramping up operations in Afghanistan, especially in the area around Kandahar City, the Taleban birthplace and their former headquarters until they were ousted from power in the US-led invasion of 2001.
NATO Secretary-General Anders Fogh Rasmussen told reporters in Copenhagen, Denmark, that higher casualties were inevitable because more troops have arrived in Afghanistan in recent weeks, bringing the overall alliance force to more than 140,000 - including 100,000 Americans.
The US figure is more than triple the number of American service members in Afghanistan at the beginning of last year.
"Right now we see more fighting and unfortunately also more casualties," Fogh Rasmussen said. "But that is the inevitable result of sending more troops... On top of that, we now attack the Taleban strongholds in Helmand and Kandahar. That of course means more fighting and unfortunately also more casualties."
British Deputy Prime Minister Nick Clegg confirmed on Tuesday that Britain's combat mission in Afghanistan would end by 2015 and pledged to protect front line troops from sudden cuts in government spending.
The US commander of the Afghan war acknowledged Tuesday that the Taleban were expanding their footprint across the country even as international forces close in on their traditional southern strongholds.
Gen. David Petraeus said a sharp rise in attacks on foreign troops showed the Taleban were feeling threatened but said there needed to be political as well as military action to wipe out the "industrial-strength insurgency."
Gen. Petraeus insisted that despite the casualties, progress was being achieved in Helmand and Kandahar.
Petraeus said he recently walked through the market in Marjah, which until last February had been a major Taleban stronghold and wholesale distribution center for opium.
He said security in Kabul had been reinforced in recent months and that five or six bases were being built for the Afghan Army around the city to protect the capital.
Nevertheless, gunmen stopped a bus Tuesday carrying clerks of the Afghan Supreme Court in south Kabul. One gunman boarded the bus and opened fire, killing three people and wounding 12, the Interior Ministry reported.
British Deputy Prime Minister Nick Clegg insisted Tuesday that the military campaign in Afghanistan was "turning the corner" as he wrapped up a two-day unannounced visit to British troops in Helmand.
"We hear so much bad news," he told British soldiers.
"Of course the country mourns when people lose their lives. People are full of anguish when there are serious injuries. But what I have seen today is a complete transformation of the military effort that I first saw when I visited two years ago."