Fighting between government forces and opponents of outgoing President Ali Abdullah Saleh on the streets of the capital Sanaa has killed one soldier, the Defence ministry said.
The violence late Friday near government buildings and the compound of Sadeq al-Ahmar, a foe of Saleh commanding significant forces, was the latest challenge to a Gulf-brokered transition plan to prevent civil war after 10 months of bloody anti-Saleh protests.
Top oil exporter Saudi Arabia shares U.S. fears more instability in Yemen would embolden the country's al Qaeda wing - against which Washington has waged a campaign of drone strikes - in a country sitting next to oil shipping routes.
The Defense Ministry, in a posting on its website, accused the Ahmar tribesmen of launching attacks in the northern district of Hasaba with the aim of derailing efforts toward establishing security and stability in the capital and other areas.
An official Friday said forces loyal to Saleh and opposition gunmen were withdrawing from the streets of Taiz city, calming a situation that threatened to wreck a political solution to months of upheaval.
Dozens have been killed in Taiz, Yemen's commercial capital, since Saleh signed a deal last month to give up power after 33 years.
A committee set up to restore normality to Taiz was clearing away road blocks set up by Saleh opponents and loyalists during street battles, and overseeing their withdrawal from occupied buildings, the official said.
More than three weeks after Saleh formally handed power to his deputy Abd-Rabbu Mansour Hadi, protesters have continued to take to the streets in anger at opposition parties' endorsement of the deal, which grants immunity from prosecution to Saleh over the killing of demonstrators by security forces.
Saleh's General People's Congress (GPC) party said it would stop holding pro-government rallies after Friday prayers to show its commitment to a political solution, and urged opposition parties to do the same.
A member of the opposition Joint Meeting Parties (JMP) said it was not for them to call off street protests, which were launched by youths who did not belong to opposition parties.
Under the transfer plan negotiated by Yemen's wealthy Gulf neighbours, the GPC and opposition parties divided up cabinet posts between them and formed a national unity government to steer the country toward a presidential election in February.
The cabinet, which is due to be sworn in Saturday, faces a host of challenges including a southern separatist movement, a rebellion in the north and the regional wing of al Qaeda that has exploited the upheaval to strengthen its foothold in Yemen.
Yemen has also faced a fuel shortage partly due to repeated attacks on a pipeline feeding its refinery. Traders said on Friday that the country was seeking to buy four cargoes of gasoline in January via a tender amounting to 120,000 tonnes to help deal with the shortages.
(Writing by Firouz Sedarat; Editing by Matthew Jones)