Colombia and that country's largest rebel group announced an agreement Sunday on one of their main bones of contention — land reform — the fruit of more than half a year of slow-moving peace negotiations in the Cuban capital.

The two sides did not release details of the agreement, but both said it constituted a major breakthrough and that it dealt with issues like property rights, access to land and rural infrastructure development.

"This agreement will be the start of a radical transformation of the countryside," read Sunday's joint communique.

The parties must now hammer out understandings in five other areas, starting with the political reintegration of Revolutionary Armed Forces of Colombia fighters, another highly sensitive issue.

Both parties have stressed that no concessions are final until a complete peace accord is reached. But for one day, at least, the long-time enemies seemed optimistic an important step had been taken toward ending the half-century long conflict.

"Today we have a real opportunity to attain peace through dialogue," said the government's chief negotiator, Humberto de la Calle. "To support this process is to believe in Colombia."

Despite the deal, rebel chief negotiator Ivan Marquez said several issues surrounding land reform still need to be worked out.

A senior official involved in the talks said the final points of disagreement revolve around the exact amount of territory that will be involved, though both sides say it will impact millions of hectares (acres). Another dispute centers on a rebel demand to limit the size of foreign holdings.

Those questions and several others will be reexamined in coming weeks as the sides discuss other issues, none expected to be as vexing. The agreement on land reform stretched to some 20 pages long, longer than the anticipated text of the rest of the peace document combined. The official spoke on condition of anonymity because he was not authorized to discuss the sensitive talks publicly.

Other major issues yet to be resolved when the two sides return to the bargaining table next month include drug trafficking and victim compensation, with the government continuing to insist that senior rebels accept jail terms as part of the peace deal.

Negotiations began in October in Oslo, Norway, and have been held in Havana ever since, with the Cuban and Norwegian governments acting as guarantors. Colombian President Juan Manuel Santos, facing criticism of the negotiations and a reelection battle in 2014, has said a deal must be reached by November or his government will pull out.

In an interview published Sunday ahead of the land reform deal, senior FARC commander Jorge Torres Victoria, who uses the nom de guerre Pablo Catatumbo, said the president's timetable may not be realistic.

"We don't want a peace process express," he told the Colombian newsmagazine Semana. "There are many big issues on which we are not yet in agreement."

The Havana talks are the fourth attempt since the 1980s to bring peace to Colombia, which has been at war ever since the rebels took up arms in 1964. A U.S.-backed military buildup that began in 2000 has reduced the FARC's ranks to about 9,000 fighters and killed several top commanders, though the rebels insist they are still a potent force.