A demolitions guy steps out into the shack you just tried to pull down. Deal with him first or he'll continue to pelt Lara with fire. Then either stay here behind the single crate...
...or move up behind the pair of crates ahead on the right, which offer a little more cover from the 2 riflemen up on the ledge to the left.
When they start shooting, release the Aim button to crouch down behind the crates where it's a little safer.
Then when they pause to reload, pop out and take a shot or two.
If you don't kill them both fairly quickly, the one on the right will move into the shack you tried to pull down. Try to take him out before he can do too much damage.