The fighting between forces loyal to both men made the past week the deadliest since mass street protests for an end to President Ali Abdullah Saleh's 33-year rule broke out three months ago. Although it could prevent bloodshed, the agreement will do little to solve the wider crisis, with Saleh rejecting efforts to negotiate his exit.
The week's battles began when Saleh's security forces attacked the home of Sheik Sadeq al-Ahmar, head of the powerful Hasid tribal confederation and an uneasy ally who abandoned the president and joined his opponents. Tribal fighters came to al-Ahmar's defense and seized a number of government buildings in the Hassaba neighborhood of the capital, Sanaa, during intense clashes.
Fighting then spread outside the capital when tribal fighters seized two army posts north of the city on Friday.
A member the committee of tribal leaders who brokered Saturday's deal said the sides had agreed to withdraw their forces from the neighborhood starting Sunday morning.
The mediation committee will take control of the government buildings seized by tribal fighters so civilians can return to the area, the mediator said.
An aide to al-Ahmar confirmed the agreement's details.
"The committee reached an agreement, and we will abide by it," he said.
Both spoke on condition of anonymity because they were not authorized to talk to the media.
The agreement late Saturday followed steps by both sides to undermine the other, with al-Ahmar calling on security forces to desert the president and Yemeni authorities issuing an arrest warrant for the tribal leader.
In a letter to security forces, al-Ahmar called on the Republican Guard and other security forces to help "get rid of this regime and be among the makers of the change that the people are calling for."
Experts say the uprising's future will be determined by the number of tribes and security forces that turn against Saleh. Many already have, including the Hashid confederation, to which Saleh's tribe belongs. Some army units have also left Saleh to back the protesters, though they did not join the fight against his forces.
The wave of defections picked up after Saleh intensified a crackdown on the protesters that has killed more than 150 demonstrators.
Al-Ahmar's letter — published online and read aloud and distributed at meetings with tribal leaders — called on others to leave Saleh.
"The enemy of all these people is Saleh, who has weighed heavily upon our people for all these years and confiscated the simplest of Yemeni citizens' rights to serve the interests of Saleh, his sons and his family," he wrote.
He called on soldiers not to "sacrifice themselves for one individual or family" and to stand with the people in choosing "change and the dream of a better future."
It remains unclear if al-Ahmar's letter will have any effect. Much of Saleh's power base is made up of childhood friends and family members he placed in high-level security posts, decreasing the chances of defection. Yemen's powerful Republican Guard, which al-Ahmar called on specifically, is commanded by one of Saleh's sons and has remained loyal to the president as other military units have defected.
The week's clashes followed a breakdown in efforts by Yemen's Gulf Arab neighbors to negotiate an end to the crisis. The deal would have required Saleh to step down in exchange for immunity from prosecution, but he balked at signing.
The Hashid turned against Saleh two months ago, throwing its weight behind the protesters. But before this week, it had kept its well-armed fighters on the sidelines.
The United States, which once considered Saleh a necessary ally in fighting an active al-Qaida branch in Yemen, has turned away from the Yemeni ruler, calling on him to peacefully transfer power.