He also said the government would be flexible in the way it implements its demand that the ELN concentrates its forces in one area as part of the deal.
Pablo Beltran, the chief ELN negotiator, said earlier in the week the group was willing to end some attacks, such as blowing up energy installations, but that to gather its fighters in one place would be "suicide".
Drug smuggling
The ELN was started in 1964 by radical students and Catholic priests inspired by Fidel Castro's Cuban revolution.
It is regarded as Colombia's most ideologically driven rebel group, in part due to its traditional reluctance to get involved in Colombia's multibillion-dollar cocaine trade.
Earlier this month Restrepo said the group had taken to smuggling drugs as its main source of income, a charge the ELN has denied.
Colombia's biggest rebel force, the 17,000-member Revolutionary Armed Forces of Colombia (Farc) has rejected conditions for starting peace talks set by Alvaro Uribe, the president. Thousands are killed in the guerrilla war every year.
Uribe scandal
Meanwhile an inquiry into politicians links to right-wing paramilitaries has continued.
Colombia's supreme court said on Wednesday that it was investigating the president of the House of Representatives and two other parliamentarians.
That followed the arrest earlier this year of eight politicians from parties in Uribe's governing coalition.
The announcement came as a further embarrassment for Uribe, who has been repeatedly accused of having close links with paramilitaries when he was governor of Antioquia province in the 1990's.
Senator Gustavo Petro also pointed to Uribe's brother, Santiago, showing politicians a picture in which he appeared with a drug kingpin, and reading testimony linking him to paramilitaries.
Santiago Uribe responded by telling a local radio station the documents "do not amount to any kind of proof."
Petro also claimed ranches owned by the Uribe family were used for meetings by paramilitary leaders in the 1990s.
Colombia's paramilitary groups were organized as private armies in the 1980s, ostensibly to protect landholders from left-wing guerrillas, but were later accused of numerous massacres of civilians, and of involvement in drug trafficking.