COLOMBIAN President Juan Manuel Santos has ordered 102 police to be transferred over last week’s massacre of protesting coca growers.

Mr Santos tweeted on Tuesday that he had instructed the nation's police director to transfer the officers out of the Tumaco municipality in Narino.

The first — albeit tacit — acknowledgement that security forces were responsible for last Thursday’s massacre came two days after narcotics police opened fire on an international investigation team.

On Monday the UN mission in Colombia said a group of its staff, accompanied by Organisation of American States observers, members of church groups and journalists came under attack while trying to reach Tumaco the previous day.

It said the team was driven back by four stun grenades, tear gas and gunfire and expressed alarm that the same police who authorised their movements had attacked them.

Vice-President Oscar Naranjo met UN representatives and apologised for the police officers' behaviour, saying they had acted "irregularly."

Witnesses now say 10 protesters were killed when police fired on farmers who formed a human chain to block a government eradication sweep against their crops. They say others remain missing.

Authorities only admit to six deaths.

National Co-ordination of Coca, Poppy and Marijuana Cultivators director Luz Perly Cordoba accused the police of “concealment” of evidence.

"There are still corpses in the area that (residents) have not been able to recover because the police are hiding evidence," she said.

The Voices of Peace organisation urged the government to implement land reform agreed under last year’s peace deal, saying the latest killings were a symptom of poverty.

“Families have had to resort historically to the cultivation of illicit crops to guarantee their vital minimums for survival,” it said in a statement.

The Defence Ministry initially tried to blame a breakaway faction of the now-disarmed Revolutionary Armed Forces of Colombia (Farc), while Mr Santos later implicated drug gangs.

At the weekend the Farc announced it had formally registered as a political party with the same acronym, the Revolutionary Alternative Forces of the Commons.

Farc leader and peace negotiator Ivan Marquez said: “The war, with its burden of pain and mourning, was left behind; we have turned this sad page.

“Now we must dedicate ourselves to reconciling the Colombian family, healing the wounds with truth.”