The decision to sign the amended peace accord was made during a meeting at a heavily guarded Catholic retreat in Bogota

Colombia’s government and leftist rebels say they will sign a modified peace agreement on Thursday despite strong resistance from former President Alvaro Uribe.

The signing ceremony promises to be a more subdued event than the heavily symbolic one attended by several heads of state in September in the colonial city of Cartagena. Reflecting the more somber mood in the country after the original deal was narrowly rejected by voters in a referendum, it will be held at the tiny Colon theatre in downtown Bogota.

The decision to sign the accord and submit it to congress for approval was agreed to Tuesday by government peace negotiators and leaders of the Revolutionary Armed Forces of Colombia during a day of closed-door meetings at a heavily guarded Catholic retreat in Bogota.

It followed a seven-hour meeting on Monday night in which government negotiators tried to persuade Uribe and other sceptics to support the accord that would put an end to a half-century of fighting with Farc.

Ever since the original deal’s defeat at the polls, Farc and government negotiators have worked around the clock introducing some 50-plus changes to make it more acceptable to conservative Colombians who overwhelmingly despise Farc.

Uribe, a still popular figure who has led opposition to the peace deal, said on Tuesday that the changes are cosmetic and that the accord, if implemented, represents a risk for Colombia’s democracy because it doesn’t go far enough in punishing rebels who committed atrocities.

He requested a meeting with Farc’s leadership to discuss his concerns, an encounter that seemed unlikely.

“Uribe governed badly, corrupted and bled Colombia during eight years and never wanted peace. He wanted to defeat Farc, but he couldn’t,” Farc commander Pablo Catatumbo, one of the rebel commanders in Bogota, wrote on his Twitter account.

President Juan Manuel Santos has made clear there is no more room for negotiation. In a joint government-Farc statement on Tuesday, negotiators said they were still working on the procedures that would be used for ratification in congress, where the government coalition has a solid majority. Uribe had been pushing for another referendum, which he expressed confidence would again vote down the accord.

The standoff comes amid concerns that a delicate ceasefire could unravel unless implementation begins soon. Last week, two suspected Farc fighters were killed in combat with security forces in a confusing incident now being reviewed by United Nations monitors.

Farc are also angry over the killings of several land reform activists and human rights defenders, three over the past weekend alone. On Tuesday Santos convened a meeting with top officials and the UN human rights envoy in Colombia to discuss the killings.

The recent murders “are palpable, dramatic evidence of the risks and uncertainty that exists around the implementation of the peace accord,” Santos said after the meeting.