Fighting in the Yemeni capital overnight between rival army units left one dissident soldier dead, witnesses and medics said on Saturday.
"Clashes broke out between soldiers from the Fourth Brigade (loyal to the regime) and the youths' security committee backed by dissident troops from the First Armoured Brigade" headed by General Ali Mohsen Al Ahmar, witnesses said.
The fighting, in which light and medium machine guns were used, took place at the eastern entrance to Change Square in Sanaa, where protesters against President Ali Abdullah Saleh have camped since February, witnesses told AFP.
"One soldier was killed and five members of the youths' security committee were wounded," said medics.
Saleh's troops fired on the square when protesters, whose numbers have been rising, tried to expand their sit-in, witnesses said.
The protesters' security committee backed by Ahmar's troops who have protected the square since March responded, they added.
Tensions have been rising in Sanaa with government forces fortifying their positions and Ahmar soldiers deployed in areas of the city they control.
On Sunday, an officer with Ahmar's troops accused the elite Republican Guard -- headed by Saleh's son Ahmed -- of shelling one of their positions in the capital.
Separately, the veteran leader's troops also fired mortar rounds overnight at the home of prominent opposition tribal chief Sheikh Sadiq Al Ahmar in Sanaa's northern Al-Hasaba district, his office said in a statement.
Six mortar rounds targeted Sheikh Sadiq's home without causing any casualties, it said.
Despite months of protests against his 33-year-long rule, Saleh, who was flown to Riyadh on board a Saudi medical aircraft after he was wounded in a bomb blast on his Sanaa compound on June 3, has refused to step down.
State news agency SABA reported on Monday that Saleh has authorised his deputy Abdrabuh Mansur Hadi to negotiate a power transfer with the opposition under a deal brokered by the Gulf Cooperation Council.
The GCC plan, proposed last spring, calls on Saleh to step down as president and transfer all constitutional authorities to the vice president. In return, Saleh would receive amnesty from prosecution for himself and his family.
At least 200 protesters have been killed nationwide since January, and the impoverished Arabian Peninsula country's economy is on the brink of a total collapse and Sanaa residents complain of prolonged power outages.