An international rights group has urged Yemeni authorities to investigate what it called "unnecessary use of lethal force" against demonstrators led by Shiite rebels in the capital who are demanding the reinstatement of fuel subsidies and the dismissal of the government.

Human Rights Watch says in a Sunday statement that Yemen's President must hold military personnel and police accountable for loss of life when they opened fire on demonstrators near the prime minister's office in Sanaa last week. Nine people were killed and 67 wounded.

Yemeni security authorities said protesters were armed and they fired at the office's security guards. HRW however quotes witnesses as saying the protesters were unarmed.

The demonstrations have escalated tensions in the capital, raising fears of wider conflict in restive Yemen.