Mumbai, Apr 20 (IANS): Amitabh Bachchan may have returned to work after his two abdominal surgeries, but pain isn't leaving the megastar. The veteran suffered stomach pain again during a dubbing session for Ram Gopal Varma's "Department".

Big B, as Amitabh is fondly called by his fans, says the constant pain is frustrating.

"Six a.m. up to dub for 'Department', but stomach strain while doing that brings back shooting pain... So frustrating," the 69-year-old tweeted early morning Friday.

Amitabh, who has been battling with health issues for long, was operated at Seven Hills Hospital in February. He was on bed rest at home for a while post his stint at the hospital. But was back to work for the opening ceremony of the fifth edition of the ongoing Indian Premier League (IPL) in Chennai earlier this month.

He is currently dubbing for "Department", which also has southern actor Rana Daggubati and Sanjay Dutt in pivotal roles.

However, due to his excruciating stomach pain, he says he is unable to give his 100 percent to work.

"The dub of a film requires great effort to catch the right tone and graph of the scene, done some many months ago. In the dark and stark confines of a dubbing theatre, with just a microphone as your co-artist, it does become quite a task," he posted on his blog bigb.bigadda.com.

"But with an injured belly and one that has suffered many, it does take its toll. So somewhere in the middle of my effort at 7 a.m. for 'Department', that sharp pain, which seems like someone slid a knife into you, returns," he added.

"Department" is set to release May 18.