WASHINGTON – President Barack Obama declared Monday he is sticking to his war strategy of using U.S. troops to advise and mentor Afghan forces, even as a suddenly growing number of Americans are being gunned down by the very Afghans they are training to take on insurgents.

In just the past 10 days, Afghan forces have attacked their coalition partners seven times, killing nine Americans. For the year there have been 32 such incidents, killing 40, compared to 21 attacks killing 35 troops in all of 2011.

"We are deeply concerned about this, from top to bottom," Obama told a White House news conference. But he said the best approach, with the fewest number of deaths in the long run, would be to stick to the plan for shifting security responsibilities to the Afghans.