Protesters seeking to oust longtime President Ali Abdullah Saleh, a key U.S. ally in fighting al-Qaida terrorists, began marching from the University of Sanaa to the Ministry of Justice, chanting: "The people want the fall of the regime."
A medical official said one man was shot in the neck and killed. He spoke on condition of anonymity because he was not authorized to speak to the press.
The capital became quiet during an afternoon period when Yemenis traditional chew a popular stimulant leaf, known as qat.
It was the 10th straight day of protests in Yemen inspired by uprisings in Egypt and Tunisia, which have killed seven people across the country. Demonstrators want the immediate ouster of Saleh, who has ruled for 32 years.
In a meeting with civic leaders, Saleh said Yemenis have the right to express themselves peacefully and that the perpetrators of the unrest were trying to seize power by fomenting instability.
"The homeland is facing a foreign plot that threatens its future," Saleh said, without elaborating. He has tried to blunt discontent by promising not to seek re-election when his term ends in 2013.
Meanwhile, residents of Yemen's port city Aden, where fierce riots have resulted in at least four deaths, said troops in armored vehicles had deployed in the main streets, at the entrances to some districts and at key buildings such as the governor's office. Many police had withdrawn from the streets, apparently to avoid confrontation with protesters who still gathered in some areas.
Vice President Abd Rabou Mansour met top officials in Aden and decided to seal off the city for a 12-hour period ending at 6 a.m. Sunday to prevent people outside Aden from joining the protests, said a security official spoke on condition of anonymity.
Earlier, residents said groups of men were looting and burning government buildings and that there was no sign of the police or armed forces.
Saleh is already facing a restless population, with threats from al-Qaida militants who want to oust him, a southern secessionist movement and a sporadic armed rebellion in the north.
To try to quell new outbursts of dissent, Saleh pledged to meet some of the protesters' demands and has reached out to tribal chiefs, who are a major base of support for him.
But a key chief from Saleh's own tribe was critical of his policies and threatened to join the protesters - an apparent attempt to pressure the embattled leader of the world's poorest Arab country.
For now, most of the protesters are students, educated professionals and activists who used social media sites Facebook and Twitter in summoning people to the streets.