A group of intellectuals who agreed to act as mediators between the Mexican government and a small leftist rebel group announced Tuesday that it will end its efforts, citing a lack of cooperation.

The commission said in a statement that the government did not do enough to help mediators try to clear up the disappearance of two rebel sympathizers in 2007. The guerrillas have accused the state of secretly holding the two men, but the government denies it.

Rebels of the People's Revolutionary Army launched a series of bomb attacks against government oil pipelines in 2007 to demand their comrades' return.

They later agreed to a cease-fire and indirect talks with the government through the mediators, but little progress was made.

The commission's statement said it "has received no help of any substance from the government."

In a statement, the Interior Department urged the commission to reconsider its decision and called for a meeting Friday to continue talks.

The department said it was surprised by the commission's decision and insisted that the government has "responded favorably to each request made."

Former mediator Miguel Angel Granados Chapa said the breakdown of the mediation effort could lead the rebels to break off the cease-fire and resume their attacks.