Larger, more sophisticated militant attacks have also caused a sharp rise in Afghan civilian deaths - at least 472 in the first seven months of the year, most in suicide bombings, according to an Associated Press count.
In all, at least 600 Afghan civilians were killed from January through July, a 30 percent increase from the same period last year, according to AP figures compiled from coalition and Afghan officials. That includes at least 128 killed by U.S. or NATO forces.
There are about 33,000 U.S. troops in Afghanistan, the highest since the war began, meaning more troops than ever are patrolling this country's mountainous terrain and exposed to ambushes and roadside bombs.
The U.S. military suffered 65 deaths in May, June and July, by far the deadliest three-month period in Afghanistan since the war began in 2001. The previous deadliest three-month period was in the spring of 2005, with 45 U.S. deaths.
In July, more U.S. troops died in Afghanistan than in Iraq for the month, for the first time since the Iraq war started in 2003. In all, 92 U.S. troops have died in Afghanistan this year, a pace that would surpass last year's death toll of 111.
The spike in violence is forcing U.S. leaders, including the presidential candidates, to call for still more troops here.
More than ever, the U.S. government recognizes the situation Afghanistan "is serious and needs to be dealt with," said Seth Jones, an Afghanistan expert at the RAND Corp., a Washington-based think tank that often does studies for the Pentagon.
"I think it is an important step that ... the gravity of the situation has been recognized and that there are some steps in place to turn the tide in Afghanistan," he said. "Whether that is successful or not is of course an open question."
Overall, at least 500 U.S. service members have died in Afghanistan, Uzbekistan, Pakistan, Qatar and United Arab Emirates in support of the Afghan mission, according to an AP analysis based on Defense Department press releases.
"In terms of milestones, it's important to point out that no casualty is more significant than any other," said Pentagon spokesman Lt. Col. Mark Wright. "Each service member is equally precious, and each loss of life is equally tragic."
The AP count is based on information from U.S., NATO or Afghan officials, often impossible to independently verify because of the remote or dangerous locations of the incidents.
The Defense Department count often lags by several days. The most recent Defense Department count, issued Saturday, showed 496 U.S. troop deaths in and around Afghanistan.
Counting coalition troops, Taliban militants and Afghan civilians, more than 3,000 people have died in violence this year, according to the AP count.
In the past, the Taliban appeared to try to minimize civilian casualties by launching its large-scale attacks primarily against U.S., NATO or Afghan troops.
But this year a February bombing at a dog fighting competition in Kandahar killed more than 100 people, mostly civilians. An attack on the Indian Embassy in Kabul last month killed more than 60.
Steven Simon, a senior fellow in Middle Eastern studies at the Council on Foreign Relations, said the recent attacks with high civilian death tolls reflect a migration of both tactics and fighters from Iraq to Afghanistan.
"The reported presence in Afghanistan of the head of al Qaeda in Iraq underscores the extent to which blowback from Iraq is being felt in Afghanistan," Simon said in an e-mail. "At this point, al Qaeda's leadership seems to be looking at the Afghan theater as the next big thing."
Afghan and U.S. officials say a big reason for the spike in violence is because militaries use sanctuaries in neighboring Pakistan where they can arm and train fighters who launch attacks across the border on U.S. and Afghan forces. More al Qaeda fighters have been using the region to launch attacks than in previous years, U.S. officials say.
Gen. Mohammad Zahir Azimi, spokesman for the Afghan Defense Ministry, blamed the rise on violence principally on two factors: a peace agreement earlier this year between the Pakistan government and some militants in its tribal areas near the Afghan border, and support given by Pakistan's intelligence agency to Taliban fighters.
Pakistan denies it is helping Taliban fighters or that it has entered into peace agreements with militants who launch attacks in Afghanistan.
Insurgent attacks have jumped by 50 percent in the first half of 2008, according to data from the Afghanistan NGO Safety Office, a Kabul-based group paid for by Western donors that advises relief groups on security.
In a report last week, ANSO said it logged 2,056 insurgent attacks in the first half of the year, a 52 percent increase from the same period last year.
The group said violence was up sharply in relatively peaceful northern and western Afghanistan and the region surrounding Kabul.
Both major presidential candidates, Democratic Sen. Barack Obama and Republican Sen. John McCain, have called for more troops to be sent to Afghanistan. President Bush has said more troops will be dedicated to the Afghan fight in 2009 but has not said how many.
U.S. military officials have said the Afghan effort needs three more brigades of troops, or about 10,500 forces.
Any new forces sent here can expect to face vicious attacks from an increasingly brazen Taliban force. Last month more than 200 militant fighters attacked a remote U.S. outpost in a dangerous and mountainous region of northeastern Afghanistan. Nine U.S. troops were killed and 15 wounded.
Even local Afghan civilians joined in on the attack, a sign the U.S. and NATO face steep challenges in their bid to win the population over to the side of the Afghan government.
"The size of the operation and the ability of the group to get support within the town was somewhat alarming, and it shows that there is clearly some concern with local Afghans, and that's a concern because civilians are the center of gravity in a counterinsurgency," said Jones. "The dangerous message is that there was involvement by the civilians."