Rangers uncovered the carcass of the dead rhino on Thursday - the day Britain's Duke and Duchess of Cambridge left India's Kaziranga National Park, a wildlife official said on Friday.

"Poachers used AK-47 assault rifles to kill the adult male rhino and after killing the pachyderm they took away its horn," Subasish Das, a senior forest officer, told the AFP news agency. He said he believes the horn was removed for sale on the black market.

Rangers also found over 100 Kalashnikov shells around the rhino's body. It was the second rhino killing at the park in the past four days.

The wildlife sanctuary in India's northeastern Assam state is home to 2,400 one-horned rhinos, which accounts for two-thirds of the planet's remaining population. The animal is currently labeled as "vulnerable," by conservation groups.

A spokesman for the royal couple said they were greatly upset by the poaching.

"The Duke and Duchess were angry to hear about the killing of this rhino during their visit," British broadcaster ITV quoted the spokesman as saying.

During their visit to the park, Kate and William highlighted wildlife conservation efforts and met with officials battling poachers in the preserve. The royals also fed baby rhinos with a giant milk bottle and observed a wild rhino during a safari tour of the wildlife sanctuary.

"They hope their time in Kaziranga encourages others to support the brave rangers that are protecting animals that are so important to the communities that surround the national park," the spokesman said.

William, who is the second-in-line to the British throne, has repeatedly condemned illegal wildlife trafficking and is a patron of the elephant conservation charity Tusk Trust.

rs/sms (AP, AFP, dpa)