Cambodian Prime Minister Hun Sen on Thursday said he had authorised the use of helicopter gunships to crack down on rampant illegal logging in an effort to curb deforestation.

Hun Sen recently appointed armed forces deputy commander-in-chief General Sao Sokha and the head of the military police to curb illegal logging and timber smuggling.

The trade, lubricated by violence and bribery of forestry officials and border guards, has eviscerated one quarter of the country's forests in a generation.

Hun Sen has been in power in throughout that time, but conservationists say he has made little headway in reducing illegal logging despite trumpeting several crackdowns.

"We recognise that deforestation must be punished. I gave two helicopters to Sao Sokha," Hun Sen said Thursday.

"I have authorised them to fire rockets."

Hun Sen said his government had also confiscated nearly one million hectares (2.5 million acres) of land from private firms in an effort to stop illegal forest clearance.

He said the trade was being conducted under the noses of officials, asking: "The logs are so big, where are the eyes of police, military police, forestry administration and the ministry of environment? Or are you guys just the same as them?"

In the last few decades a surge in illegal logging has contributed to a sharp drop in Cambodia's forest cover, which fell from 73 percent in 1990 to 57 percent in 2010, according to the United Nations.

Probes into the lucrative trade are steeped with risk and several high-profile killings of activists trying to expose the rampant spread of logging have blighted the kingdom in recent years.

A forest ranger and a policeman who were investigating illegal logging in Cambodia were killed in November and at least 10 people, including a soldier, were arrested over the murders.

In its haste to develop the impoverished nation, the government has been criticised for allowing firms to clear hundreds of thousands of hectares of forest land -- including in protected zones -- for everything from rubber and sugar cane plantations to hydropower dams.

Rights groups and environmental watchdogs have linked many of these concessions to rampant illegal logging, and say armed government forces often act as security guards for offending companies.

Environmentalists met Hun Sen's latest order with scepticism.

Ouch Leng, a Cambodian forest activist, said Hun Sen had repeatedly launched similar crackdowns "but the illegal logging has continued".

"Cambodia has lost nearly all of its forest," he said.

Demand for rare woods from wealthy Chinese and Vietnamese is believed to have spurred much of the deforestation in the Mekong region.