Yemeni security forces fired upon crowds of anti-government protesters Monday, leaving at least 12 dead and causing numerous casualties.
Witnesses say plainclothes police and snipers shot at the demonstrators in the town of Taiz after they surged into a square facing government headquarters.
Foreign media footage showed protesters drenched in blood as makeshift hospitals were set up to treat the wounded.
Witnesses report that dozens of protesters were also wounded during clashes in the Yemeni cities of Hodeida and Beyda.
Meanwhile, the New York Times reports that the United States is dropping its support for President Ali Abdullah Saleh and is negotiating the terms of his departure.
Unidentified U.S. and Yemeni officials say the U.S. position changed over a week ago, when the talks began.
The president has offered to step down but only after new elections are held. His current term ends in 2013. He has been in power for 32 years.
A Yemeni official told the Times says the negotiations center on a proposal in which Saleh would hand over power to a provisional government led by Vice President Abd al-Rab Mansur al-Hadi until new elections are held.
The violence comes a day after another demonstrator was reported killed Sunday in Taiz when police opened fire on anti-government protesters. Scores more were wounded.
Yemen has seen increasingly bloody protests against longtime ruler Saleh since late January. Saleh recently called for an end to the protests and said he is willing to discuss the peaceful transfer of power "according to the constitution."
Some information for this report was provided by AP, AFP and Reuters.