* Separatist movement denies involvement
* Police say 30 protesters arrested
By Fumbuka Ng'wanakilala
DAR ES SALAAM, May 27 (Reuters) - Hundreds of supporters of a separatist Islamist group set fire to two churches and clashed with police during protests in Zanzibar over the weekend against the arrest of senior members of the movement, police and witnesses said.
Police accused the Uamsho (Awakening) group of ordering its supporters on to the streets - but the movement's leadership denied having any part in the unrest.
Clashes broke out in the historic commercial and tourism centre of Stone Town on Saturday night and continued until Sunday afternoon, witnesses told Reuters.
The reports of attacks on churches will raise fears of an escalation in religious tensions in the predominantly Muslim island ruled by a semi-autonomous secular government. Several bars were attacked last year.
Shops remained closed and people stayed in their homes on Sunday as riot police patrolled the streets of Stone Town, witnesses said.
"There is a lot of tension, people are hiding in their houses. All the streets are empty, it's the only the police who are out there," resident Mai Zuberi told Reuters by phone.
"There were clashes all night on Saturday and the violence continued until noon today. All the roads were blocked in the Stone Town area," Zuberi added.
Police said they had arrested 30 members of Uamsho - a Swahili acronym of its full name the Association for Islamic Mobilisation and Propagation. Uamsho has called for a referendum on Zanzibar's exit from its union with mainland Tanzania.
"We will continue to search for more leaders of the Uamsho group, which was responsible for inciting these riots," Zanzibar Police Commissioner Mussa Ali Mussa said in a statement on Sunday.
"One church was extensively burnt by the protesters, and the second was partially burnt and the protesters were prevented from completely destroying it," he told Reuters by phone separately.
The group dismissed the accusations. "The Uamsho association ... is not involved in any acts of breach of peace. We would like to urge all Muslims and Zanzibaris to continue to maintain peace and tranquillity in the country," it said in a statement.
The Indian Ocean archipelago of about 1 million people merged with mainland Tanganyika in 1964 to form the modern Tanzania, but Zanzibar retains its own president and parliament.
Tanzania, which has enjoyed relative stability in a volatile region, has pledged to have a new constitution in place by 2014, with the union expected to be one of the major issues of debate.
Analysts said the Uamsho group has been gaining popularity following the disenchantment of supporters of Zanzibar's main opposition Civic United Front (CUF) party after its decision to form a government of national unity with the ruling Chama Cha Mapinduzi (CCM) party.
"We should never allow a few disgruntled people to plunge us into chaos over religion so as to achieve their own political goals," mainland Tanzania opposition lawmaker Zitto Kabwe said in a statement. (Editing by George Obulutsa and Andrew Heavens)