As many as 50 demonstrators were killed by Yemeni security forces in recent days. The reported deaths of at least 21 people during clashes Monday coincided with the arrival of top diplomats who were in the country to discuss plans for political transition.
U.N. Secretary-General Ban Ki-moon, in a statement issued through his spokesman's office, said he was "gravely" concerned about escalating violence in Yemen. Ban added that he "strongly" condemned the "excessive use of force" against civilian demonstrators in Sanaa.
Yemeni President Ali Abdullah Saleh, in a decree issued from Saudi Arabia last week, gave his vice president authority to conduct talks that would eventually lead to a democratic transition of power.
Ban urged all political players in Yemen to work closely the members of the Gulf Cooperation Council and the United Nations to find a peaceful solution to the political crisis.
Catherine Ashton, the European Union's high representative for foreign affairs, in a statement, said the violence highlights the need to find a solution to a political impasse that's been simmering for most of the year.
"Perpetrators of the violence should be held accountable," she added.