Nepalese officials said on Wednesday a lovesick elephant which has trampled several people to death was captured a month ago -- but was set free to kill again.

Park rangers told AFP the male tusker, named Dhrube by locals, had been targeting humans on a killing spree in southern Nepal after being kept from potential mates, including a female called Chanchalkali.

"It has killed another male elephant and was upset after it was denied the chance to mate with Chanchalkali," Chitwan National Park ranger Bishnu Thapaliya told AFP.

The elephant is suspected of killing at least nine people inside the park over four years, Thapaliya said, and up to six who have been trampled after it was captured and then released a month ago.

Rangers removed its tusks after it was suspected of killing two people in separate incidents in mid-November -- but they then attached a tracking device and set it free.

"We were monitoring but could not locate it. But when we downloaded the data and analysed it, we were shocked because it had wandered into places where people had been killed," Thapaliya said.

"It had walked over 150 kilometres (95 miles) away from the park. It had even gone to India. In Bara district, two people were killed by an elephant on November 26, which we assumed was by another elephant. But it turned out that Dhrube was there during that period.

"Similarly, two Indians were killed by an elephant on the India border on November 28 and again the data suggested that it was there too."

The Nepalese army launched a shoot-to-kill hunt after the animal dragged a couple in their 60s out of their hut and trampled them on Saturday. But soldiers and park staff have been unable to track it down despite its tag.

The beast first came to the attention of authorities five years ago when it destroyed an army post in an attack on soldiers in Chitwan, 150 kilometres (95 miles) south of Kathmandu.

The tusker, named after the army post, is accused of killing a soldier in Chitwan soon afterwards.

Rangers suggest the animal went rogue after being prevented from mating with females in Chitwan at least twice in recent years.

"This elephant has strayed from its herd. Others usually destroy crops but this one goes straight for humans and kills them," Thapaliya told AFP.

The elephant has also been nicknamed Valentino after a St Valentine's Day attack on the luxury Tiger Tops safari resort in 2010.

Nepal has about 300 elephants, including around 100 domesticated adults which take tourists on jungle rides.