UNITED NATIONS, May 1 (Reuters) - Secretary-General Kofi Annan expressed concern on Friday about a flare-up of fighting between the Tajikistan government and Islamic opposition forces and called on both sides to work together to restore calm.

A statement issued through a U.N. spokesman said the U.N. Mission of Observers in Tajikistan, a 70-member unit helping monitor a tenuous accord signed last June, reported severe fighting east of Dushanbe, the capital, and within the eastern city limits.

It said the fighting, which erupted on Wednesday, was apparently triggered by the arrest of three opposition members.

''The secretary-general is very concerned at this flare-up of hostilities, which carries the risk of escalation. He calls on the government and UTO (United Tajik Opposition) to work together to stop the fighting and to restore calm,'' the statement added. Annan is on an African trip.

The Tajikistan government said on Friday it had driven rebel troops from Dushanbe as the army stepped up three days of fighting in the mountainous Central Asian state.