Yemeni government forces and opposition fighters began withdrawing from parts of the southern city of Taiz on Monday after four days of shelling and clashes that killed at least 20 people, witnesses and activists said.

The pullout follows the establishment, under a deal designed to end months of protests against President Ali Abdullah Saleh, of a military committee intended to curb fighting between forces loyal to Saleh and his foes.

Since the morning, we have seen tanks and armoured vehicles being pulled away from positions in the eastern part of Taiz, said Tawfiq al-Shaabi, an activist in a protest encampment in central Taiz. We also noticed that (opposition) fighters have gone from the streets, he added.

A protester demanding Saleh face trial was shot dead and at least one other wounded in the city, witnesses and activists said. Saleh would have immunity from prosecution under a power transfer deal he signed last month.

The tanks have withdrawn from the area near the traffic department, but plainclothes snipers are taking their place. The situation is still unstable, said protest leader Bushra al-Muqtari.

Prime Minister-designate Mohammed Basindwa, an opposition leader who is to form a government shared with members of Saleh's party, had said his side would rethink its commitments under the transition deal if the fighting in Taiz did not stop.

(Reporting by Mohammed Ghobari; Writing by Sami Aboudi; Editing by Peter Graff)