KOLKATA, India, Aug 4 (Reuters) - Indian police forced a thief to gobble down 40 bananas in a few hours, hoping they would force him to excrete a gold necklace he had snatched and swallowed.

Sheikh Mohsin, 35, grabbed the 45,000-rupee ($1,115) necklace from a woman in the eastern city of Kolkata on Friday and popped it into his mouth when police and local residents caught him.

"He denied swallowing it at all, but an X-ray conducted in a hospital revealed the necklace was very much in his stomach," Ajay Kumar, a leading city detective, told Reuters.

"Doctors advised us to feed him with bananas as it worked like a natural purgative," another officer said, trying to keep awake after staying up all night monitoring Mohsin's motions.

Mohsin visited the lavatory three times early on Saturday and was also forced to vomit but the necklace has failed to appear.

"We will have to look for other stronger purgatives now," the yawning police officer added.