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KABUL, Afghanistan - U.S. and NATO commanders say they have blunted the Taliban's threatened spring offensive, killing almost 40 commanders and 2,000 insurgents. But suicide bombings and civilian deaths inflicted by international forces are all on the rise, threatening to derail the five-year mission to pacify and rebuild Afghanistan.

Six months into 2007, claims of progress in stabilizing the government of President Hamid Karzai are clouded by strains in the Western alliance and what analysts say is growing pessimism in NATO capitals.

Five years after the Taliban's ouster, the militia is again a serious adversary, seizing control of swaths of the south, despite the presence of more NATO, U.S. and Afghan troops.

In a possible additional setback, U.N. and other Western officials expect this year's opium-producing poppy crop to exceed last year's record haul, mostly because of a spike in Helmand province, the world's largest poppy-growing region and also perhaps the most violent part of Afghanistan.

Two Afghan officials from Helmand on Sunday said 45 civilians and 62 insurgents were killed by NATO and U.S. airstrikes in their province Friday night. NATO admits some civilians were killed but says that estimate is far too high. Karzai ordered a six-man team to investigate.

The military insists increased fighting this year reflects their own more muscular approach. However, there is doubt that the bloodletting will pave the way for the Western-backed government to assert control over longtime Taliban strongholds and allow foreign troops to go home.

"I feel there is a growing air of pessimism, but I don't think there is anything inevitable about it," said Joanna Nathan, Afghanistan analyst for the International Crisis Group, a nonprofit research group.

"I do not feel it's lost at all, but at the same time I feel it requires a hard look at the strategies here," she said.

U.S. and NATO commanders say they quashed Taliban hopes of a spring blitz with offensive operations of their own, including an ongoing British-led effort in the southern province of Helmand.

"There has been a spring offensive and I think it's been NATO's," U.S. Gen. Dan McNeill, the top NATO commander in Afghanistan, told The Associated Press this month.

The alliance had expected more bombings and suicide attacks, "But as to ground maneuver, a combination of fire and maneuver, more classic operations, the offensive has been NATO's," he said.

The U.S. and NATO say the insurgents' use of Iraq-style tactics is a sign of desperation -- that the Taliban have lost 39 commanders, including its ruthless southern commander, Mullah Dadullah, and close to 2,000 fighters.

Other figures tell a different story.

In eastern Afghanistan, attacks were up 83 percent during the first half of the year compared with the same period of 2006, according to the U.S. units who operate there.

Suicide bombings in the east roughly tripled, though military officers say the onslaught has been largely ineffective.

"If this is the spring offensive, things are going to be just fine," said U.S. Col. Martin P. Schweitzer, a NATO commander in the east.

Yet the Taliban has managed to kill 94 international troops, including 46 Americans in six months, and appears to have no difficulty finding recruits to make up for its own heavy losses. On June 17 a bomb in a police academy bus in Kabul killed 35 people -- the deadliest such incident since the U.S.-led invasion in 2001.

Contributing to the increased violence is a higher number of international troops. While there were virtually no international forces in Helmand and Kandahar provinces in early 2006, there are now more than 6,500. The U.S. also added a combat brigade, roughly 3,500 troops, in the east.

The Taliban's military strategy -- moving away from head-on confrontation and instead relying on ambushes and bombings -- is becoming more like al-Qaida's, said Mustafa Alani, director of security and terrorism studies at the Dubai-based Gulf Research Center.

NATO and Afghan troops are finding that a frustrating challenge. "We don't have an enemy to fight face to face," Afghan Col. Abdul Satar said on an operation in Ghazni province last week.

The military must also deal with public opinion both in Afghanistan and NATO countries.

Last year Taliban militants killed far more civilians than U.S. or NATO military actions, but the trend has reversed this year, in part through the aggressive use of Western air power.

In Iraq, the U.S., with 160,000 troops there, mounted 266 airstrikes in the first five months of 2007. The 50,000 international forces in Afghanistan used four times more -- 1,032 airstrikes, according to the U.S. military.

A U.N. tally shows that of civilian deaths this year, 314 were caused by international or Afghan security forces, and 279 by insurgents. A similar AP count, though lower, shows the same trend: 213 killed by the U.S. or NATO and 180 by the Taliban.

Overall, the AP counts almost 2,800 people killed this year. The tally, based on Western and Afghan official data, puts the violence far ahead of last year, when about 4,000 died.

Qari Yousef Ahmadi, who contacts foreign media by satellite phone and says he speaks for the Taliban, warned that thousands have volunteered for suicide bombings and that civilians should stay away from military convoys.

"The Taliban are increasing attacks, suicide bombings, ambushes against U.S. and NATO forces," Ahmadi said. "These suicide attackers are not highly trained, but they have a spiritual calling," he said.

U.S. officials note that the Taliban have launched no operation comparable to the one outside Kandahar last fall in which more than 1,000 insurgents battled NATO forces.

Still, Dutch and Afghan forces needed air support to fend off about 500 Taliban fighters attacking the town of Chora last month, and McNeill said insurgents have showcased new, advanced maneuvers during ambushes this year.

Though the Afghan army is gaining strength, few believe it is close to being strong enough to protect the Western-backed government without foreign help.

"I think everybody has to realize that it's not going to be won quickly or lost quickly, insurgencies are not," the International Crisis Group's Nathan said. "What we need here are long-term commitments."