Somalia's 25 presidential hopefuls were campaigning ahead of an election due Monday, the final stage of a UN-backed process to set up a new administration for the war-torn country.

The election has been delayed several times -- having already missed an August 20 deadline -- but international pressure has increased on parliament to chose a president swiftly, setting the date for Monday.

"We are only days away from an historic presidential election," UN special representative for Somalia Augustine Mahiga said earlier this week, praising efforts to 'move forward to a new more legitimate and representative' system.

Analysts have taken a far gloomier outlook on the process, suggesting it offers little but a reshuffling of key figures and positions.

Somalia has lacked an effective central government since president Mohamed Siad Barre was ousted in 1991, unleashing cycles of bloody conflict that have defied countless peace initiatives.

Ruthless warlords and militia groups including Al-Qaeda-linked Shebab insurgents have controlled mini-fiefdoms that African Union troops and other forces have only recently started to capture.

Outgoing president Sharif Sheikh Ahmed, in power since 2009, is one of the favourites, though he cuts a controversial figure with Western observers.

A UN report in July said that under his presidency, 'systematic embezzlement, pure and simple misappropriation of funds and theft of public money have become government systems' -- claims Sharif has rejected.

Former prime minister Abdiweli Mohamed Ali, a US-educated economist, is also another strong candidate for the post.

"The future of Somalia depends on each and every legislator voting for whomever they believe can best lead their country," Mahiga added. "I encourage them to carry out this sacred trust free from any external influence."

The new parliament, whose members were selected last month by a group of traditional elders, will vote in a secret ballot in up to three rounds. Each candidate had to pay $10,000 (7,900 euros) to enter the race.

Bitter arguments have begun between rival challengers, divided along Somalia's notoriously fractious clan lines, and the United Nations Security Council has issued repeated warnings of 'intimidation and corruption'.

The council has warned of its 'willingness to take action against individuals whose acts threaten the peace, stability or security of Somalia'.

However, Britain's ambassador to Somalia Matt Baugh said earlier this week that both the outgoing president and prime minister -- key candidates for the top job -- had assured him of 'their commitment to respect (the) election outcome'.

The voting will be overseen by newly elected parliamentary speaker Mohamed Osman Jawari, a veteran politician and former minister.

A candidate needs to take two-thirds of the vote to win outright, otherwise the top four candidates will go into a second round, with a third round of the final two. The winner is selected by a simple majority.

The political developments come as African Union and Somali troops make significant gains against the hardline Shebab, although they remain a major threat. Ethiopian troops are also battling them from the south and west.

The extremist insurgents in August abandoned the port of Marka, leaving the Shebab with two major ports in southern Somalia -- Barawe and the rebel bastion of Kismayo -- although an international naval blockade has already greatly squeezed maritime access there.

The Shebab a year ago abandoned their last fixed bases in Mogadishu, where they have since reverted to guerrilla tactics, claiming a series of suicide attacks and roadside bombs.