A 40-year-old man with known Crohn's disease, currently in remission on azathioprine, presents with a 2-day history of severe, colicky right iliac fossa pain, vomiting, and abdominal distension. He has not opened his bowels for 3 days. Abdominal X-ray shows dilated loops of small bowel with multiple air-fluid levels. What is the most likely diagnosis?