By Karen Allen BBC News, Zanzibar

A bigger military presence can be seen ahead of Zanzibar's vote

Zanzibar, famous as the Indian Ocean's Spice Islands, comprises a cluster of islands including Pemba to the north and Unguja, better known as Zanzibar island, to the south.

Having gained independence in 1963, it became part of mainland Tanzania the following year and now enjoys considerable autonomy, having its own parliament and president, as well as sending elected representatives to the mainland.

For the past two elections since multi-party voting began the ruling party, the CCM (Chama Cha Mapinduzi), has dominated - but there are considerable numbers in Zanzibar who feel this ruling elite has sidelined the wishes of the islanders.

This time round the opposition CUF (Civic United Front) is confident it will clinch power.

At its colourful campaign rallies - where supporters sport the red, white and blue party colours and chant their party slogan, "truth" - there is an air of optimism.

This is a party that feels it has been denied power twice, after previous elections in 1995 and 2000.

On both occasions there were widespread allegations of vote rigging. Dozens were killed in the clashes that ensued the last time people cast their vote.

The worry is that similar violence could be repeated in Zanzibar this time around.

'No tampering'

Only last week the Zanzibar Election Commission found that 2,000 "bogus" names had been added to the electoral register, and the opposition CUF has expressed fears that the military is being used to intimidate voters and will be involved in the collection of ballot boxes once votes are cast.

But Idrisa Jecha, a spokesman for the commission, said the military had been called upon because of its logistical experience and insisted there was nothing underhand about the arrangements.

"The party agents are allowed to be there to see everything, even to follow the military convoy up to the registration centres, so I don't know how the army can tamper with the ballot papers," he said.

A team of Commonwealth observers has been monitoring events all week.

Those sporting the green and yellow colours of the ruling CCM, unchallenged since multi-party elections began, argue their party has brought development, social housing and tourism to the islands.

But frustrations about the elaborate relationship with mainland Tanzania, coupled with deep-rooted ethnic tensions, have helped to establish the CUF's powerbase in Zanzibar.

Supporters of the ruling CCM party say it has brought development

There have been attempts to link the CUF to radical Islam - something its presidential candidate Seif Sharif Hamad robustly rejects.

Many of its supporters will use their vote not because they follow a party ideology, but simply to protest against a ruling party they feel has dominated for too long.

It is an incongruous sight to catch a glimpse of the green army uniforms alongside the tourists meandering down the narrow streets of Stone Town, the main administrative centre of Unguja.