BOGOTA (Reuters) - Colombian President Juan Manuel Santos and opposition rival Alvaro Uribe met on Wednesday in a bid to resolve differences over a peace deal with Marxist FARC rebels that was unexpectedly rejected in a plebiscite, leaving the country in limbo.

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The two expressed willingness to seek an end to the 52-year war that has killed more than 220,000 people and displaced millions more.

Sunday’s shock referendum result, which confounded pollsters and was a political disaster for Santos, plunged the country into uncertainty over the future of the Revolutionary Armed Forces of Colombia (FARC) rebels, who had been expected to disarm once the deal was passed by voters.

After more than three hours of talks, former President Uribe emphasized the need for “adjustments and proposals” to ensure the deal includes all Colombians.

Without giving any concrete proposals, Uribe, 64, said Santos had shown he was disposed to changes.

Uribe, a former lawyer and cattle rancher, opposed Santos’ peace talks from the start and said the final deal, which was reached in August after four years of painstaking negotiations in Havana, gave too many concessions to the rebels.

He spearheaded the “no” campaign, urging Colombians not to approve the accord, which would have given the FARC guaranteed congressional seats and immunity from traditional jail sentences. “No” carried the day by less than half a percentage point.

“We identified that many of their worries come from points that need clarification or precisions. Today we began to work with them to firm up those points and resolve their doubts,” Santos said in a brief statement.

The future of the deal seems to hang on whether the FARC will accept tougher conditions for demobilization, perhaps combined with a softening of Uribe’s hard-line demands.

Santos once served in Uribe’s cabinet, but the two have not met since late 2010.

The government has said the decision to re-open talks lies with rebel leadership.

Government negotiators are in Havana to confer with guerrilla commanders who have said they will remain “faithful” to the accord.

Thousands, many wearing white, marched in cities across the country in support of the deal on Wednesday. Members of Santos’ cabinet joined marchers in Bogota’s main square.

A senior U.S. State Department official said both sides are committed to dialogue.

“They have made it clear they want the peace process to continue and they want to negotiate a settlement,” the official, who met with both sides, told reporters.