U.S. troops in Afghanistan now have far-reaching new protections against rogue killers among their Afghan allies, including assigned "guardian angels" -- fellow troops who will watch over them as they sleep.

Marine Gen. John Allen, the top U.S. commander in Afghanistan, ordered the added protections in recent weeks to guard against insider threats, according to a senior military official. They come in the wake of 16 attacks on U.S. and coalition forces by Afghans that now represent nearly one-fifth of all combat deaths this year.

Some of the changes have been subtle, others less so.

In several Afghan ministries, Americans are now allowed to carry weapons. And they have been instructed to rearrange their office desks there to face the door, so they can see who is coming in, said the official, who spoke on condition of anonymity to describe the orders.

Two U.S. military officers working in the Afghan Interior Ministry, one of the most heavily guarded ministry buildings in Kabul, were gunned down at their desks on Feb.