A poll published Sunday indicated that Colombians would reject a peace deal to end the country's half-century civil war in a planned referendum.

Just 39 percent of respondents backed the peace deal and 50 percent opposed it, in the study by polling firm Ipsos published by Colombian media.

The government wants citizens to endorse its accord with the country's biggest rebel force, the Revolutionary Armed Forces of Colombia (FARC).

The two sides laid the groundwork for a full peace deal when they signed a definitive ceasefire in June.

They hope that deal will soon be followed by a full peace accord if such an agreement is approved in a referendum in the coming months.

But many Colombians are wary of a deal that would see FARC fighters reintegrated into society without being tried over the bloodshed.

Former president Alvaro Uribe has been campaigning fiercely for a "No" vote against the peace deal.

A similar poll last month had shown a majority in favor of a deal, but that trend appeared to have reversed on Sunday.

President Juan Manuel Santos and his government have been negotiating for an accord since 2012.

But his approval rating has dropped sharply -- it stood at 25 percent in Sunday's poll.

Many voters said they did not want former FARC leaders to go into politics under the accord and said they must go to jail for their crimes.

Around 260,000 people have been killed in the territorial conflict in Colombia that started in 1964.