BOGOTA (Reuters) - Colombia’s Senate has backed a law to regulate transitional justice under the country’s peace deal with Marxist FARC rebels, including special tribunals that will try guerrilla leaders for war crimes.

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The law, approved late on Wednesday, is considered the cornerstone of the agreement signed last year between the government and the FARC, known then as the Revolutionary Armed Forces of Colombia. The measure still needs approval from the lower house of Congress, which is likely to vote on it early next week.

The special courts will mete out alternative sentences like landmine removal for ex-guerrilla leaders who are convicted of war crimes. Under the peace deal, those convicted will not serve time in traditional jails.

The law can also apply to members of the military and civilians who funded illegal groups like paramilitaries.

Congress has until the end of the month to approve the law using the court-approved “fast-track” mechanism to reduce the number of required debates in an effort to implement the peace accord as quickly as possible.

In a move that invigorated the previously slow debate in the Senate chamber, the nation’s top court ruled this week that the majority of the law, including provisions that allow former rebels to participate in politics, is constitutional.

The court made several modifications however. A provision in the agreement prohibits extradition of former FARC members, but the ruling said that only applied to crimes that occurred before the deal.

It said ex-rebels who commit crimes after demobilization would be subject to regular laws that include the possibility of extradition.

That did not sit well with the FARC, which is now officially a political party.

“The extradition prohibition as it stands in the final accord is a right and not a benefit,” senior FARC member Ivan Marquez told journalists on Thursday. “Making the prohibition ineffectual constitutes a flagrant and very grave non-compliance with the deal.”

Under the agreement the FARC will have 10 guaranteed seats in Congress until 2026. The group has already announced a slate of candidates for elections next year.