The Colombian government and leftist Farc rebels have announced a major breakthrough in peace talks aimed at ending nearly half a century of conflict, heralding a "radical transformation" of the war-ravaged countryside.

The two sides said in a joint communiqué that they had reached an agreement on land and rural development issues, the first point in a peace process launched six months ago.

The lead government negotiator, Humberto de la Calle, said the agreement would represent "a historic change, a rebirth of the Colombian countryside".

Land rights and distribution are at the heart of the conflict in Colombia, which saw Farc rise up against the state in the mid-1960s claiming to fight on behalf of the country's peasants. Today 52% of farms are in the hands of just over 1% of landowners, according to the UN Development Programme, giving Colombia one of the most unequal land distributions in the world.

According to official figures, only 22% of potential arable land is cultivated and 6.5m hectares of land was stolen, abandoned or forcibly changed hands in other ways between 1985 and 2008 as a result of the conflict.

Sunday's agreement "seeks to reverse the causes of the conflict" and would be the "start of radical transformations in Colombia's rural and agrarian reality", according to the statement read in Havana, where the negotiations have been taking place since November.

As part of the deal, Colombia would create a land bank through which farmland would be redistributed. Farmers would receive loans, technical assistance and marketing advice as well as legal and police protection.

Specific points of the agreement – such as how many hectares of land would be available for redistribution under the accord – were not made public. However, De la Calle said legal landowners had nothing to fear.

The vagueness of the announcement has triggered opponents of the government to question the process. Rafael Guarín, a critic of the peace talks and of the government of Juan Manuel Santos, tweeted: "What did Santos give in exchange for the Farc's 'yes' on rural and territorial issues?".

Farc has said it wants to see 9m hectares of land set aside for "peasant reserve zones" that would enjoy some autonomy from national government control. The government rejected the idea of autonomous zones but said they could be the focus areas of rural development programmes.

The government and rebel negotiators stressed they would enter into effect only if an overall peace accord was reached.

The chief Farc negotiator, Iván Márquez, said several issues surrounding land reform remained unresolved but the agreement was most likely announced to show some progress in the talks, about which many Colombians remain sceptical.

If the land issue was difficult because of the technical nature of the subject and the historical context, the next items on the agenda may be even more complicated politically. When the talks reconvene on 11 June, negotiators will begin to tackle the problem of how Farc can make the transition from an 8,000-strong guerrilla army to a legitimate political movement.

Farc tried this before with disastrous results. As part of a previous peace process in the mid-1980s it created the Patriotic Union party to participate in electoral politics while the rebels remained in arms.

But as many as 3,000 of party its members, including two presidential candidates, were murdered in the process. On the other hand, a majority of Colombians find it unpalatable to see rebel leaders sitting in Congress. Two-thirds of Colombians polled in April said they would not accept Farc leaders participating in politics if the group demobilised.

Other items on the agenda include the drug trade – a major source of funding for the rebels – reparation of victims, demobilisation, and implementation of a final accord. Santos, who faces re-election in May 2014, has said he wants to see a final peace deal ready by November.

Despite the tight deadline, De la Calle is optimistic. "Today we have a real opportunity to achieve through dialogue," he said.