The peace agreement Colombia is negotiating with leftist FARC guerrillas may not be finalized by a March 23 deadline, the UN envoy to the country said Wednesday.

Fabrizio Hochschild said however he hoped the agreement between the government of President Juan Manuel Santos and the Revolutionary Armed Forces of Colombia could be reached "in the first half of this year."

Both sides earlier agreed to a March 23 deadline for a deal to end a half-century conflict. Peace talks currently being held in Cuba began in November 2012.

"I believe that it is possible that in order to reach a final agreement, with all the details resolved... perhaps a bit more time will be needed," Hochschild said.

Colombia and the FARC have yet to agree on the details of disarmament and the manner the final accord will be ratified.

Santos wants to put the peace deal to a popular vote, but the FARC wants it passed by a constituent assembly.

Hochschild described this "very difficult" stage as "the last kilometer of a marathon."

Nevertheless, unlike three other failed attempts at peace, "there is trust that this time an agreement will be reached," Hochschild said.

Talks appeared to be in peril over the weekend as Santos and the FARC leaders squabbled over restrictions on the rebel leaders' movements in Colombia.

However on Wednesday Cuba and Norway -- two of the peace process guarantors -- said in a joint statement in Havana that the crisis has been defused.

"An agreement has been reached to overcome recent difficulties" and resume peace talks in Havana, the statement read.

"All of the commitments agreed to by the parties regarding de-escalation and confidence building measures will continue to be implemented," it said.

The crisis was resolved after Norwegian Foreign Minister Borge Brende traveled to Bogota, and later Havana where he met Cuban Foreign Minister Bruno Rodriguez.

The United Nations has agreed to send a political mission of unarmed observers to monitor disarmament and the transition to peace once an agreement is reached.

The FARC was launched in the aftermath of a peasant uprising in 1964 and authorities estimate it currently has some 7,000 members.

The Colombian conflict has drawn in right-wing paramilitaries, drug traffickers and several leftist rebel groups, and has left more than 220,000 people dead.