Rob Pattinson is packing on the pounds!

Okay, so he appears to have added just one or two ... but the British actor is hitting the gym! We've spotted him with his trainer multiple times this past week so he's definitely on a regimen of weights and workouts -- getting serious about his upcoming role in Mission Blacklist, the story of how the military found Saddam Hussein.

Rob will play Eric Maddox -- a military interrogator fresh out of training who has "a unique ability to decipher highly complex patterns from seemingly random events," according to Production Weekly. "His mission is to trap the world’s most wanted man, Saddam Hussein – and he must defy his superiors to uncover his prey. The closer he gets to the truth, the more dangerous the hunt becomes."

We CANNOT WAIT! Suspense, intrigue, and Rob Pattinson in uniform ... sign me up!