TUMACO, Colombia — The deal that ended decades of war in Colombia hinged on a simple formula: The rebels would surrender their weapons, and in exchange, earn the right to run for office in the country’s democracy.

But on Friday the former fighters said they were suspending their campaign. Their activists were being killed, they said, and threats were mounting against those who remained — including their top commander who is running for president.

While the decision does not send the country back to war, it does put Colombia’s peace into a kind of limbo. The former rebels’ involvement in this year’s elections was meant to signal an end to decades of political violence and was a pillar of the accords that ended 52 years of civil conflict.

Their sudden departure from the campaign — on the grounds that it is not safe — casts doubt on whether the conflict is over yet.