KABUL, Afghanistan -- On the eve of the final "fighting season" before the major pullout of American troops from Afghanistan begins, U.S. deaths here have fallen to their lowest levels in five years.

The decline is ever steeper for international forces: The NATO-led International Security Assistance Force suffered its fewest number of troops killed in December, January and February in seven years.

U.S. deaths in those months this winter totaled 17, down from 57 the previous winter.

As of Friday, a Marine who died in Helmand province on Feb. 22 was the only U.S. service member to be killed in 43 days, the longest such stretch since the winter of 2006-07, according to records kept by iCasualties.org, which tracks deaths in the wars in Iraq and Afghanistan.

The main reason for drop in deaths among the coalition troops, military leaders say, is that Afghan security forces have reached nearly full strength and increasingly are taking the lead in fighting insurgents. Also, measures taken to stop so-called insider attacks by Afghan soldiers and police officers on their foreign allies apparently have been effective.

Such insider attacks reached a deadly crescendo last summer, and there were 47 attacks last year, which caused 62 deaths, according to the ISAF. But there have been just two such deaths in nearly four months: a British soldier who was killed in early January and an American civilian contractor whom an Afghan policewoman shot in December.

"There has certainly been an improvement in the past six months and we feel like those countermeasures have been effective, though it’s of course too early to make a final judgment," said German Brig. Gen. Gunter Katz, the spokesman for the international forces in Afghanistan.

Both the international forces and Afghan commanders took steps to mitigate the attacks, he said. One such step was stronger security, including stationing armed ISAF troops called “guardian angels" whenever foreign and Afghan troops mix.

Katz also said that better cultural training for international troops and Afghan security forces had led to better understanding. For example, ISAF soldiers now are taught not to ask their Afghan counterparts about their wives, which may anger conservative Afghans. The Afghans, meanwhile, are taught to expect such questions.

"The Afghan Ministry of Defense actually printed brochures where things like this are explained, where it says if ISAF soldiers ask you about your wife, they don’t mean to offend," Katz said.

The NATO-led foreign forces and Afghans also increased intelligence-gathering to identify security officers’ links to the Taliban, and the Afghans tightened their enlistment standards to do a better job of catching applicants with links to the insurgents.

The reduction in the number of international forces here also probably had an effect, Katz said.

"Compared to last summer, we have about 30,000 to 35,000 troops less, and just based on the numbers, you would assume the attacks would go down some," he said.

With the winter months ending, however, casualties are expected to rise as fighting intensifies in Afghanistan’s rural areas, as they have every year since the war began late in 2001.

Afghan forces inevitably will get the worst of it this year. The fall in casualties among U.S. and NATO troops, which started three years ago and has accelerated, comes at the expense of the Afghan security forces now doing much of the fighting. About 3,400 Afghan soldiers and national police officers were killed last year, a jump from about 1,950 the previous year, according to a tally in January by the Brookings Institution.