Yemeni Nobel Peace Prize winner Tawakkul Karman joined about 100 protesters Tuesday outside the United Nations to call for President Ali Abdullah Saleh to stand down.
"We came here to tell that Ali Abdullah Saleh and (Syrian leader) Bashar al-Assad are both criminals and they have to be held accountable and prosecuted," Karma said.
"People are living on sidewalks and are being killed everyday... All because they asked for democracy and justice.
"These regimes are a danger to international security," she added, speaking through a translator.
Karman, who shared the 2011 Nobel prize with Liberian President Ellen Johnson Sirleaf and "peace warrior" Leymah Gbowee also from Liberia, has called on the United Nations to act immediately to halt the Yemeni government's crackdown on pro-democracy protests.
"As a Yemeni leader, as a Nobel Prize winner, as a leader of the Arab Spring, I came here to tell them to stand up for these rights," Karman said.
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"We're calling on them to treat the revolutions in Yemen and Syria just like they did in Libya.
"I feel shamed that tonight I will be sleeping in a hotel and my people will be sleeping in the streets."
She plans to hand a letter to UN Secretary-General Ban Ki-moon on Wednesday, and she has called on the International Criminal Court to investigate the actions of the Yemeni government.
Karman and tens of thousands of other pro-democracy activists have camped out in Sanaa's Change Square for months, marching against Saleh despite a violent crackdown by government troops that has killed hundreds since the mass protest movement began in late January.
At least seven protesters were killed and dozens wounded on Tuesday as gunmen loyal to Saleh opened fire on demonstrators in the Yemeni capital, medics and the opposition said.
It was the third time in four days that demonstrators had attempted to march from their base in Change Square on loyalist-held areas of the capital to be met by deadly gunfire.
Despite months of protests and international pressure, Saleh has refused to end his 33-year rule and step down despite a plan drawn up by the Gulf monarchies for a peaceful transfer of power.
At least 861 people have been killed and 25,000 wounded since protests first erupted, according to a letter from Yemen's youth movement sent to the United Nations earlier this month.