KABUL - A veteran commander of top-secret special operations takes charge of the nearly 90,000 U.S. and NATO troops in Afghanistan Monday, promising to limit the civilian deaths that have cost Western troops Afghan support.

General Stanley McChrystal arrived in Afghanistan on Sunday, a month after being named by President Barack Obama to succeed General David McKiernan, abruptly removed last month from command of a war U.S. officials say is not being won.

The measure of effectiveness will not be (the number of) enemy killed, it will be the number of Afghans shielded from violence, NATO quoted McChrystal as saying in a statement.

After his arrival, McChrystal met Afghan President Hamid Karzai, who pressed him to avoid civilian casualties, Karzai's office said.

Civilian deaths by foreign troops while hunting the militants, nearly eight years on since the Taliban's ouster, have angered many Afghans and have been the main source of friction between Karzai's government and the United States.

It is an issue both sides have been stressing, especially since a U.S. air strike in May that the Afghan government says killed 140 civilians, mostly children.

Washington acknowledges mistakes in that strike and says 20-35 civilians died along with about 60 people it believes were fighters.

Washington considers Taliban-led insurgencies in Afghanistan and neighboring Pakistan to be its main security threat, and has begun diverting tens of thousands of troops to Afghanistan from Iraq.

McChrystal takes command midway through a massive build-up of U.S. forces that will see their numbers more than double from 32,000 at the end of 2008 to an anticipated 68,000 by the end of this year.

He also commands about 30,000 troops from other NATO allies.

U.S. forces say the number of insurgent attacks in Afghanistan is at its highest since the militants were driven out of power in retaliation for shielding Osama bin Laden after the September 11 attacks on the United States.

Fighting is expected to intensify over the next months as more U.S. and NATO troops deploy ahead of an August presidential election.

McChrystal's background has raised some eyebrows: for most of the last six years he led a cadre of super-secret U.S. special forces raiders in both Iraq and Afghanistan, tasked mainly with locating, capturing and assassinating insurgent leaders.

Much of his career is classified, and an official biography released by NATO leaves out many details.

But in an interview with the Wall Street Journal this month, he said he had learned that targeted killings, like those he has carried out for much of his recent career, were not enough to defeat an insurgency.

Since 9/11, I have watched as America tried to first put out this fire with a hammer, and it doesn't work, he said. Decapitation strategies don't work.

You're going to have to convince people, not kill them.

(Writing by Peter Graff; Editing by Jerry Norton)