The cubs fathered by Cecil the lion are being protected by his brother Jericho amid fears they will be killed by a male rival, researchers said today.

The much-loved lion was killed by American dentist Walter Palmer earlier this month, sparking outrage around the world.

After his death, there were fears his cubs would be killed by the next lion in the hierarchy so he could father his own offspring with the females in the pride.

But a team at Oxford University's Wildlife Conservation Unit, which had been studying Cecil before he was shot dead, said the lion's brother had stepped in to safeguard the young.

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Father's cubs: Cecil the lion with his offspring before he was cruelly killed by an American dentist

Cecil's pride: A couple of Cecil's cubs relaxing in the Hwange national park back in 2012. It was initially feared that the cubs would be killed if another male lion took over the pride

Project leader David Macdonald said: 'The natural law in lion society is that when a male dies and his weakened coalition is usurped, the new incoming males kill their predecessors' cubs.

'This may not happen because Cecil's brother is still holding the fort.'

Macdonald had warned earlier this week that Cecil's death could lead to a 'cascade of other deaths'.

He said: 'At a personal level as I have watched this lion... and gloried in his magnificence and beauty. I was very deeply saddened by this.

'To the extent that it was illegal it was completely reprehensible.

But I hope that some good might come out of it in terms of raising the profile of lion conservation around the world.'

Johnny Rodrigues, Chairman for Zimbabwe Conservation Task Force, confirmed that Jericho was keeping the cubs safe from any rival males.

Speaking to the Mailonline, Mr Rodrigues said: ' Everything is fine, Jericho has taken over the pride and all the cubs are safe.'

He also said that if the pride was going to be taken over and the cubs killed, it would have happened several weeks ago when Cecil was killed.

Brutal: Cecil the lion (right) fights with a rival male in May last year. Since his death, there have been fears that his cubs would be killed by a rival male, but they are reportedly being guarded by Cecil's brother Jericho

Cecil the lion (right, darker mane) fighting with a rival lion on safari at the Ngweshla Picnic site at the Hwange National Park in Zimbabwe

Palmer has admitted killing the 13-year-old predator, who was fitted with a GPS collar as part of the Oxford University study.

But he said in a statement he had hired professional guides and believed all the necessary hunting permits were in order.

He has not been sighted since his identity was revealed by Zimbabwean conservationists earlier this week.

Zimbabwe today called for Palmer to be extradited from the United States after accusing him of killing the much-loved animal illegally.

Environment minister Oppah Muchinguri said the dentist should be handed over to Zimbabwean officials to face justice, adding that she understood prosecutors had started the legal process to make that happen.

Referring to the 55-year-old trophy hunter from Minnesota as a 'foreign poacher', she said: 'We are appealing to the responsible authorities for his extradition to Zimbabwe so that he can be made accountable for his illegal actions.'

Hunter: Palmer had is now under investigation after he admitted killing the lion (not pictured) in Zimbabwe this month

Zimbabwean Environment minister Oppah Muchinguri (left) has called for American dentist Walter Palmer (right) who shot Cecil the lion to be extradited from America after accusing him of killing the animal illegally

Muchinguri also said Palmer's use of a bow and arrow to kill the lion, who is said to have been lured out of Hwange National Park with bait before being shot, was in contravention of Zimbabwean hunting regulations.

Professional Zimbabwean hunter Theo Bronkhorst insisted he did nothing wrong on the hunt that killed Cecil the lion, telling AFP he was shocked to find the animal was wearing a tracking collar.

'I don't believe I failed in any duties at all, I was engaged by a client to do a hunt for him and we shot an old male lion that I believed was past his breeding age. I don't think that I've done anything wrong,' Bronkhorst said

He said: 'Both I and the client were extremely devastated that this thing had a collar on because at no time did we see a collar on this lion prior to shooting it.

'We were devastated... I left the collar there at the bait site and unfortunately that was stupid of me and negligent of me.'

Bronkhorst was granted bail by the Hwange court on Wednesday after being charged with 'failing to prevent an illegal hunt' when he led the expedition in early July.

Palmer, a life-long big game hunter, managed to return to the United States before the authorities were aware of the controversy around Cecil's death.

'It was too late to apprehend the foreign poacher because he had already absconded to his country of origin,' Muchinguri said.

The killing has sparked social media outrage against Palmer in the United States.