Cecil's son, Xanda, who was six years old, was apparently shot dead on around July 7 just outside a national park in Zimbabwe, not far from where his father was killed two years ago, various sources said Friday.

"Xanda was shot by a trophy hunter on a legally sanctioned hunt in a hunting area outside Hwange National Park," Andrew Loveridge, a researcher from Oxford University's zoology department told the news agency AFP.

"As researchers, we are saddened to lose a well-known study animal we have monitored since birth," he added.

Both Xanda and Cecil, who researchers say had at least 12 surviving cubs last year, were being monitored by the Oxford University's wildlife conservation research unit through GPS tracking collars.

Each of the two lions was killed after straying out of the national park into a legal hunting area. Xanda was the head of a pride with two lionesses and several cubs.

'Legal hunt'

Richard Cooke, the safari operator who organized the hunt for an unnamed client, confirmed to DPA news agency that Xanda had been killed.

"The hunt was legal and the collar was returned. That's all I can say at this stage," Cooke said.

Trophy hunters from the United States, Europe or South Africa often pay such operators tens of thousands of dollars for the chance to kill lions and other wild animals.

Defenders of the practice say that hunting provides an essential economic incentive to promote long-term conservation and that revenue pays for safeguarding wildlife and catching poachers.

Read more: Trophy hunting - Lives or livelihoods?

'Senseless and cruel'

Not everyone appears convinced by these arguments, however, and Walter Palmer, the US dentist who reportedly paid $50,000 (42,932 euros) for the opportunity to kill Cecil, was forced to temporarily close his dental practice and go into hiding amid a massive international outcry against the shooting.

The World Animal Protection action group also spoke out against the killing of Xanda.

"This shows once again that the world must urgently act to protect animals in the wild," the Africa Director of the group, Tennyson Williams, said, describing the killing as "senseless and cruel."

"Trophy hunting often leads to prolonged suffering and fuels demand for wild animal products, leaving them open to further exploitation."

The citizens' initiative World Heritage Species also slammed the practice of trophy hunting in comments on Facebook.

"This is the same senseless and tragic story that we had with Cecil, while at the same time the tired and unsubstantiated argument regarding the benefits of trophy hunting continues," it said.

tj/rt (AFP, dpa)