UNITED NATIONS Secretary-General Ban Ki-moon Sunday expressed great concern over the deteriorating situation in Yemen and condemned the excessive use of force by security forces against peaceful demonstrators in Sana'a. Ban called for utmost restraint and urged the Government and opposition groups to reach an understanding on initiating genuine and broad-based dialogue to avert a further deterioration of the security situation. The Secretary-General calls on the Government of Yemen to uphold international human rights standards and to investigate allegations of extrajudicial killings and human rights violations, said a statement issued by his spokesperson. Media reports said that Yemeni police attacked demonstrators in the centre of Sana'a, killing some six people and injuring many others. Hundreds of police reportedly used tear gas, water cannon and fired live bullets at protesters gathered in a square in the city. Agencies add: the US expressed deep concern over escalating violence in Yemen, where at least three people were killed in bloody clashes between security forces and protesters Sunday. The White House chided US allies Yemen and Bahrain on Sunday for violence used against protesters in those countries and urged both to exercise restraint. "We urge the govts of these countries to show restraint, and to respect the universal rights of their people," the White House said in a statement. "We urge the government of Bahrain to pursue a peaceful and meaningful dialogue with the opposition rather than resorting to the use of force."