Forest rangers in northeast India shot dead two poachers on Wednesday at a wildlife sanctuary where 13 threatened one-horned rhinos have been killed in the past two months, an official said.

Four men entered Kaziranga National Park, 200 kilometers (120 miles) from Assam's main city Guwahati, early Wednesday and fired at a rhino, park warden N.K. Vasu told AFP.

The shot, which missed its target, alerted forest guards who rushed to the spot.

"A fierce encounter took place between the two sides in which two of the poachers were killed," Vasu explained, adding that a rifle had been recovered.

Last week forest rangers engaged in a gun battle with poachers for more than seven hours, but they failed to prevent the killing of another rhino whose valuable horn was gouged out.

Wildlife experts say the price of a single rhino horn rivals gold and its value attracts international organised crime groups.

China is the main market, where it is used for medicine and jewellery while in Vietnam many believe that rhino horn can cure cancer and has aphrodisiac qualities.

At least 21 rhinos were killed in Kaziranga National Park last year by the poachers.

A 2012 census in the park put the number of the rhinos at 2,290 out of a global one-horned rhinoceros population of 3,300.

The species fell to near extinction in the early 1990s and is currently listed as "vulnerable" by the International Union for Conservation of Nature, one notch away from "endangered".