Threats of violence and flawed legislation are undercutting Colombia's efforts to return huge swaths of land illegally snatched from poor farmers during the country's half-century conflict, according to a study released Thursday.

Amnesty International's report said that titles to less than 74,000 acres (30,000 hectares) have been granted to victims since the country enacted a land restitution law in 2011. That's a fraction of the 19.8 million acres (8 million hectares), an area the size of Costa Rica, that the government estimates was stolen mostly by paramilitaries but also leftist rebels and other armed groups during the bloody conflict that still rages in parts of Colombia.

One of the biggest obstacles to returning land to original owners is the lack of security, the London-based group said. At least 35 land activists and people involved in the restitution process have been killed since the law's passage — one of the latest victims was a government-hired topographer who was shot while working on a case.

Poor government coordination and the lack of funding for judges and special tribunals responsible for mediating disputes also make it harder to fend off claims from powerful agribusinesses that in some cases have been occupying properties illegally for years.

In the rare cases when a land title is granted, families who were forced off their land as much as two decades ago lack the resources to sustainably resume farming.

President Juan Manuel Santos' government has acknowledged many of the problems, which it says stem from the decision to begin the reparations process as violence still rages in many parts of the countryside. Historically unequal land distribution was a major driver of Colombia's conflict and one of the key components of peace negotiations taking place the last two years in Cuba between the government and the Revolutionary Armed Forces of Colombia.

"In many parts of the country the state is only arriving for the first time," said Ricardo Sabogal, head of the government's Land Restitution Unit. "No other country in the world has tried doing this before fighting ends."