Colombia's president said Tuesday he hoped this week to seal a permanent ceasefire that would clear the way for a peace deal ending a half-century conflict with leftist rebels.

President Juan Manuel Santos called for a "last effort" by negotiators to settle the final points at peace talks between his government and the Revolutionary Armed Forces of Colombia (FARC).

"I pray to God to give us the strength to conclude those agreements, hopefully this very week, because we are on the verge of settling them," Santos said in a public speech.

He referred to the last remaining items on the agenda at the peace talks in Havana.

The talks have made progress over the past year, after the FARC declared a unilateral ceasefire in July 2015.

But the sides have so far failed to agree on the final details of how to implement the accord, including a definitive ceasefire and disarmament.

"If the negotiators make a last effort to conclude that definitive point, the ceasefire and ending hostilities, we will have made a fundamental step to achieving peace," said Santos, who hopes a full peace deal can be sealed by July 20.

The Colombian conflict started as a rural uprising in the 1960s and has drawn in various armed groups and gangs over the decades.

It has left 260,000 people dead and 45,000 missing, according to official figures.