Updated

A proposal to annul an amnesty for officials of Uruguay's former dictatorship fell one vote short in the country's Congress on Friday after a bitter debate that reopened divisions from the 1973-85 military government.

The ruling center-left Broad Front party had pushed to overturn the amnesty for soldiers, but one of its congressmen abstained, leaving it one vote short of a majority in the 99-seat legislature.

Hundreds of leftist activists ringed the Congress building to demand an end to the amnesty that had protected soldiers from prosecution for kidnappings, killings and other abuses committed by the dictatorship.

Veterans groups, meanwhile, were rankled by the fact that the measure would have left intact a similar amnesty for Marxist guerrillas who fought both the dictatorship and the elected civilian governments that preceded it.

The amnesties were meant to help Uruguayans reconcile after a long period of conflict, and before the vote, Mujica, himself a former rebel, raised questions about how the military might respond. He warned that scrapping the amnesty would create "political dangers that may be impossible to overcome."

But in an interview on Channel 10 television Friday, the president said the outcome was "a shame" and added that the amnesty question remained an issue.

"I did my best to gain the political decision, but it was not possible," Mujica said.

Hours after the vote, thousands marched through the center of Montevideo demanding information on the fates of detainees who "disappeared" during the dictatorship. A peace commission found in 2003 that 29 prisoners were secretly killed in Uruguay in that era and about 150 Uruguayans met the same fate at the hands of a junta in neighboring Argentina.

The Supreme Court ruled in 2009 that the amnesty for dictatorship officials was unconstitutional and the Inter-American Court of Human Rights ruled this year that Uruguay must remove roadblocks to prosecuting crimes against humanity.

Human rights groups argue the official amnesty allows government crimes to go unpunished, and Broad Front members say that the government's "dirty war" continued long after the Tupamaro guerrillas had been defeated.

The issue has divided this small country of 3.5 million people almost down the middle.

Uruguay's Senate approved the measure to annul the amnesty by a single vote in April. Two popular plebiscites to overturn the amnesty failed to win majorities, but by thin margins. Forty-six percent voted to overturn the amnesty in 1989 and 48 percent voted for the measure in 2009.

A peace commission found in 2003 that the dictatorship killed 175 leftist political activists, 26 of them in clandestine torture centers.

But the Tupamaros also committed killings, kidnappings, robberies and other attacks after taking up arms in 1963 against democratically elected governments. They were defeated a decade later.

Leftist activists on Friday commemorated those who died under the dictatorship. The day marks the anniversary of the 1976 murder of two Uruguayan congressmen who were killed while in exile in Argentina after a military government seized power there and cooperated with the soldiers running Uruguay in attacking leftists.