Hundreds rallied in Yemen's capital on Tuesday, anniversary of the 2011 killing at least 45 protesters, demanding that former president Ali Abdullah Saleh and aides be tried for their deaths.
Amnesty International meanwhile called for revoking the immunity granted to Saleh under a UN-brokered deal through which he stepped down in 2012, and for an independent probe into human rights violations committed the year before.
On March 18, 2011, dubbed the "Friday of Dignity," gunmen loyal to Saleh shot dead 45 protesters, most of them university students, and wounded another 200 in just three hours, according to figures compiled by Human Rights Watch.
This was at the start of a popular uprising against Saleh's three-decade rule inspired by the Arab Spring, which swept veteran rulers from power in Tunisia and Egypt.
After a year of protests and clashes between demonstrators and forces loyal to Saleh, the Yemeni leader stepped down in February 2012 under a deal that granted him immunity from prosecution.
Young activists have rejected the deal, and continue to stage rallies demanding justice.
Holding up symbolic coffins, Tuesday's demonstrators chanted "no immunity for the killers" and "Saleh and his aides should be put on trial."
The demonstration was organised by the Youth Revolutionary Council, one of the groups that led the year-long uprising against Saleh.
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A statement read at the demonstration in Sanaa's Change Square, the epicentre of the anti-regime protests, called for the sacking of Attorney General Ahmed al-Awash, a Saleh appointee. They accuse him of covering up for the perpetrators of the attack.
London-based Amnesty said that Awash had refused to investigate Saleh and other senior officials.
“The immunity law is totally unacceptable and must be revoked immediately. Effectively it allows anyone guilty of human rights violations associated with the previous government to walk free,” said Amnesty International's MENA director Philip Luther.
Luther said President Abdrabuh Mansur Hadi's promises to set up an independent probe into the attack "remain unfulfilled.”
“By dragging their feet over ensuring a full and impartial investigation into these deaths, Yemen’s authorities are sending a disturbing message that justice and accountability are not a priority for them,” Luther said.
He allowed that Yemen "has begun to introduce some promising human rights reforms."
"But sustainable reform cannot be achieved without justice for victims and their families. If the government wishes to prove that it is serious about human rights, they must tackle entrenched impunity,” said Luther.
Saleh is still head of his General People's Congress party, and critics accuse him of trying to hamper the country's political transition.