Yemeni security forces shot and killed at least two people from a restive Shi'ite group and wounded 30 others on Sunday when they opened fire on demonstrators protesting against a security branch accused of abuses, the group said.
In a separate incident, a local official said a U.S. drone had killed three suspected al Qaeda members.
The Yemeni government is struggling with an Islamist insurgency linked to al Qaeda; with a separatist movement in the south; and with Shi'ite Houthis demanding more say in the future of Yemen, a U.S.-allied state adjoining top oil exporter Saudi Arabia.
Abdel Karim al-Khaywani, a local Houthi leader, said members of his group had demonstrated outside Yemen's external security service in Sanaa demanding that it be disbanded because of its involvement in suppressing political activists under ousted president Ali Abdullah Saleh.
"Police used live ammunition and at least 14 were wounded," Khaywani told Reuters. He later said the number of wounded had risen to 30 and that two people had died in hospital. He accused police of arresting some of the wounded before they could be treated.
But a local security source said police had only fired at civilians who had fired on them first, and that a number of suspects had been detained. The source said the wounded were being treated at a local hospital.
The Houthi group, which draws its name from the tribe of its founder and leader, fought the government off and on for control of parts of northern Yemen from 2004 until a truce was reached in 2010.
The group, which still controls parts of the north and is engaged in reconciliation talks with Sanaa, played a key role in the popular uprising that forced Saleh to step down in 2011, and has since been reinforcing its presence in the capital.
Last week, tens of thousands of members reburied the remains of their founding leader, Hussein al-Houthi, nine years after he was killed during the fighting in 2004.
Separately, in the northern province of al-Jouf, a pilotless U.S. plane fired missiles at a vehicle containing suspected al Qaeda militants, killing three, a local Yemeni official said.
The official gave no further details of the identity of the militants or what they were doing.
President Obama has been criticized in the United States for the use of drone strikes that have led to civilian casualties.
In a speech on May 23, he pledged that such strikes would be limited to "continuing and imminent" threats, and said the Defense Department would take over the lead in launching drone strikes from the Central Intelligence Agency, meaning there would be more Congressional oversight.