Colombian officials said on Monday that 17 civil campaigners have been murdered over the past two months in the country, amid tensions over its contested peace process.
President Juan Manuel Santos has warned that fresh violence could destabilise the demobilisation of the leftist Revolutionary Armed Forces of Colombia (FARC) rebels under a historic peace accord.
He signed the deal with FARC and pushed it through the legislature in December, defying criticism from conservative rivals. In the weeks following, reports emerged of killings by local civil campaigners by unidentified groups in conflict areas.
On Monday the Victims' Unit, a state conflict resolution body, said in a statement that "17 civil leaders have been murdered since December 1, after Congress ratified the peace accord".
The last known victim was Porfirio Jaramillo, leader of a group demanding rural land restitution. He was killed on Saturday in Antioquia department, in the north-west, it said.
Land rights were at the heart of the conflict that pitted the Marxist FARC against Colombian state forces since 1964.
The peace agreement reconciles the two main rival forces in the war, but there are fears of score-settling between renegade players in the multi-sided conflict.
As well as leftist rebels and state forces, the conflict drew in right-wing paramilitaries backed by landowners.
They were supposedly disbanded in the 2000s but the FARC and other groups say former members of them are still active.
The Victims' Unit said Jaramillo was taken away from his home by four armed men. Police found his dead body on Sunday morning.
"We are extremely worried by these events because the truth is they are massacring social leaders," the unit's director, Alan Jara, said in a statement.
He called on prosecutors to investigate the killings and urged authorities to provide protection for social group leaders.