Since they opened in Havana on November 19 2012 the talks have produced partial deals on three out of six agenda items: land reform political participation for the rebels and fighting the drug trafficking fueling the conflict in the world's largest cocaine-producing country.

And they appeared to take a leap forward last September 23 when negotiators announced a deal on one of the thorniest issues of all -- meting out justice for the atrocities that rights groups say have been committed on both sides in a conflict that has killed more than 220000 people and uprooted six million.

"Peace has arrived!" the Marxist guerrilla group said that day just before a historic handshake between Colombian President Juan Manuel Santos and the leader of the Revolutionary Armed Forces of Colombia (FARC) Timoleon "Timochenko" Jimenez.

It was a picture-perfect moment both men dressed in white -- the politician who has staked his presidency on the peace process and the guerrilla leader who is technically still wanted on terrorism charges.

They topped it off by vowing to sign a final accord within six months.

But that optimism has since soured.

The FARC accuses the government of trying to backtrack on the justice deal while continuing to kill rebel fighters on the ground despite their unilateral ceasefire.

In response the guerrillas have hedged on the March 23 peace deadline saying the six-month countdown will only begin when the justice agreement is finalized.

The rebels' chief negotiator Ivan Marquez warned recently that "difficulties" at the negotiating table risked making the peace process "a failure."

Cautious optimism -

Even if the two sides cement a deal they have yet to agree on how to adopt it.

The government insists the final accord be put to a vote by the Colombian people in a simple "yes or no" referendum.

The rebels want to write it into the constitution so it can never be watered down.

And there are other obstacles along the way starting with the justice issue.

"The main challenge right now is settling the justice question: determining how many years of prison guerrilla fighters who have committed atrocious crimes will have to serve" said Jairo Libreros of the Universidad Externado de Colombia.

Other unsettled issues include the rebels' eventual disarmament and its corollary: security for ex-combatants in a country still rife with violence from a conflict that has also drawn in drug traffickers right-wing paramilitaries and other leftist rebel groups.

The latter include the smaller but still-active National Liberation Army (ELN) which has yet to enter into peace talks.

Still there is widespread hope that these talks -- the fourth attempt at peace since the FARC's founding in 1964 -- will eventually reach a deal.

A recent Gallup poll found 52 percent of Colombians are optimistic the talks will yield a peace accord.

"Yes it is possible to imagine a peaceful country and a better future" Marquez said Wednesday.