The United Nations' human rights agency says it has received reports that Yemeni troops have killed more than 50 anti-government protesters in the city of Taiz since Sunday.
Human rights chief Navi Pillay on Tuesday condemned the government's intensified use of force on protesters, calling its acts "reprehensible" and urging the government to make sure the human rights of its citizens are protected.
She also criticized security forces for occupying a hospital in Taiz and destroying a field clinic near the protesters' camp. Pillay said medical staff and facilities should never be targeted by government forces.
European Union foreign affairs chief Catherine Ashton said Tuesday she is "shocked" by the use of force and live ammunition against peaceful protesters and condemns it "in the strongest terms." She called for immediate steps toward political transition in Yemen.
Meanwhile, fighting continues in Taiz, and it restarted Tuesday in the capital, Sana'a, indicating the breakdown of a truce between tribal leaders and forces loyal to President Ali Abdullah Saleh.
Pillay's agency said it has also received reports about the dire situation in the southern coastal town of Zinjibar, where government forces launched air strikes after it was seized by Islamist militants Sunday. More than 30 people are reported to have died in fighting there, including four soldiers.
On Monday, Yemeni forces killed more than 20 opposition demonstrators in Taiz. Republican Guard troops and plainclothes gunmen backed by tanks moved in before dawn, opening fire on crowds in the city's main square where protesters had been camped out for weeks. Witnesses say Yemeni troops shot at protesters, set fire to tents, and crushed a field hospital as they took control of the square.
The U.S. embassy in Sana'a condemned what it called the "unprovoked and unjustified attack on youth protesters."
Also Monday, Yemeni security officials said they are searching for three French aid workers who have been missing in the southeastern province of Hadramout since Saturday. The officials said investigators have located a vehicle used by the aid workers outside a town in the province.
The French Foreign Ministry says it appears increasingly likely that the aid workers were kidnapped. They were working for a France-based aid group Triangle Generation Humanitaire.