By Marc Frank and Helen Murphy
HAVANA/BOGOTA (Reuters) - Colombia's government and Marxist guerrillas went back to the drawing board in Havana on Tuesday after a peace deal they painstakingly negotiated over four years was rejected in a shock referendum result.
In a vote that confounded opinion polls and was a disaster for President Juan Manuel Santos, Colombians narrowly rebuffed the pact on Sunday as too lenient on the rebels.
Lead negotiators Humberto de la Calle and Sergio Jaramillo were back at a Havana convention center on Tuesday meeting counterparts from the Revolutionary Armed Forces of Colombia (FARC) to see what the rebels are willing to do, the government said.
The Cuban capital was the venue for talks between the two sides since 2012 that reached an accord to end Colombia's 52-year war that has killed around a quarter of a million people.
All sides, including "No" voters, who carried the day on Sunday by less than half a percentage point, say they want an end to war, and the two parties have kept their ceasefire.
But there is vehement opposition - led by hardline former President Alvaro Uribe - to major planks of the previous deal, including guaranteed congressional seats for the FARC and immunity from traditional jail sentences for leaders.
A renegotiation seems to depend on whether the FARC would accept tougher conditions, maybe combined with a softening of Uribe's demands. After years of refusing to meet negotiators, Uribe has now said he is willing to seek a joint solution.
Colombian Foreign Minister Maria Angela Holguin said the decision whether to officially renegotiate the accord lies with the FARC.
On Monday the rebels said they would remain "faithful" to the negotiated accord and Twitter messages from FARC leadership appeared to suggest reluctance to change the terms at this stage.
"The thing is, just as the government has its deal breakers, so does the FARC, so we have to see if it is willing to reopen the accord," Holguin told reporters.
"There was no Plan B, we believed the nation wanted peace."
Three representatives from Uribe's right-wing Democratic Center party are to pore over details with three from the government. In what may turn into a dual negotiation process, those meetings are to commence once de la Calle returns from Cuba.
Colombian financial markets fell on Monday as investors worried that the limbo over the peace deal would hold up fiscal reforms such as tax changes.
Finance Minister Mauricio Cardenas, however, said the tax reforms would go ahead.
(Additional reporting by Julia Symmes Cobb; Writing by Andrew Cawthorne and Helen Murphy; Editing by Alistair Bell and Frances Kerry)