Four Kenyan policemen were to be charged with illegal possession of ivory at a Nairobi court Tuesday, the government's wildlife agency said in a statement.

The four junior officers, who are all members of a special unit tasked with ministerial security, were arrested on Monday evening in a government-owned vehicle while attempting to sell five kilogrammes (11 pounds) of ivory, with a market value of around $5,500 (5,000 euros).

A statement from the Kenya Wildlife Service (KWS) said the suspects -- three bodyguards and a driver -- are members of the Security of Government Buildings Unit of Kenya's Administration Police.

Poaching in Kenya is on the wane with environment minister Judy Wakhungu saying last week that the number of elephants killed in 2015 had fallen to 93 from 164 in 2014.

But the east African country remains an important smuggling route for illegal ivory with large shipments of tusks from poached elephants being shipped out of Mombasa port.

The trafficking is facilitated by corruption, with criminal gangs paying off police, customs officials and judges.

A five-year study of wildlife cases before the Kenyan courts, carried out by conservation organisation Wildlife Direct and published in 2014, found that only seven percent of those convicted of offences against elephants and rhinos actually went to jail, despite the crimes carrying a maximum 10-year sentence.

More than 30,000 elephants are killed for their ivory every year in Africa to satisfy demand in Asia where raw tusks sell for around $1,100 (1,000 euros) a kilogramme.

Kenya plans next month to torch its vast stockpile of 120 tonnes of ivory, eight times the size of any ivory stockpile destroyed so far.