London - Former British prime minister Margaret Thatcher, 83, underwent an operation on her upper arm, following a fall, at a London hospital Friday.

Her son, Mark, said the surgery to insert a pin into a bone had been "successful."

He said he was "delighted and relieved," given his mother's age and the fact that general anaesthesia was required.

Doctors decided to insert the pin after the injury failed to heal as quickly as they would have liked.

Thatcher would be released from hospital at the earliest next Wednesday, he said.(dpa)