HARARE (AFP) - Elephants attacked and killed a veteran ranger on patrol in Zimbabwe's largest game reserve, Hwange, where over 300 pachyderms have been poisoned since July, a wildlife official said on Tuesday.

The 61-year-old ranger was killed by three elephants on Monday when he stepped out of his patrol base to "relieve himself", the wildlife authority said in a statement.

Zimbabwe officials have beefed up game park patrols after reporting that more than 100 elephants were killed by poachers using cyanide poisoning in recent months. An independent wildlife conservation group puts the toll at 325.

Twelve people have been arrested in connection with the killings and five have already been handed prison sentences of a minimum of 15 years each.