At least seven people have been killed and at least 30 wounded in a gun fight next to the National Security Agency building in the Yemeni capital, Sanaa.
The violence broke out as Shia Houthi rebels attacked the national security building with automatic weapons and grenades on Sunday, Al Jazeera's Mohamed Adow reported.
The protesters were demanding the release of political detainees, an official told AP news agency, adding that they fired at guards while trying to storm the intelligence headquarters.
He said some of the detainees were arrested for smuggling weapons and drugs. He spoke on condition of anonymity according to regulations.
Meanwhile, Ali al-Bokhayti, a Houthi leader, said only five members of the group were killed. He blamed the security forces for the deaths, accusing them of using excessive force.
|Al Jazeera's Mohammed Adow reports from Sanaa
In another part of the country, a military official said an airstrike on Sunday, believed to be a US drone attack, killed three suspected al-Qaeda fighters in the eastern province of al-Jawf, bordering Saudi Arabia.
The official said two missiles were fired at two cars carrying the suspected fighters in the al-Mahashma area in al-Jawf.
A US airstrike in al-Jawf in 2011 killed two US-born al-Qaeda activists - cleric Anwar al-Awlaki and Samir Khan, who edited al-Qaeda's internet magazine.
In the southern province of Hadramawt, one soldier was killed and three others injured in an ambush by al-Qaeda fighters on Sunday, a military official said.
He said the army, backed by warplanes, pressed its operation against al-Qaeda in Hadramawt, killing two fighters, bringing to nine the number of fighters killed since the start of the offensive on Wednesday.
The incidents happened a day after Yemen began a second round of national dialogue in Sanaa, aimed at drafting a new constitution and preparing for elections next year.