The threat from terrorism and piracy in Somalia are among the issues that will be discussed at a conference in London on the future of the country.
Representatives from 40 countries will attend the event, aimed at devising a common approach to a country blighted by years of civil war and famine.
The leaders are expected to agree money for schools, hospitals and the police.
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The UK has described Somalia as the “world’s worst failed state” but said it needs a “second chance”.
Somali Prime Minister Abdiweli Mohamed Ali, among a number of senior government figures attending the event, has warned the country is at a “critical juncture” and needs more international help.
US Secretary of State Hilary Clinton, Nigerian President Goodluck Jonathan, Ethiopian leader Meles Zenawi and UN secretary general Ban Ki-moon are among the leaders due to join the discussions.
On Wednesday, the UN Security Council approved a resolution increasing the number of African Union (AU) troops in Somalia by 5,000 to more than 17,000. Council members also agreed to extra funding for the mission and to extend its mandate.
At the same time, Ethiopian and Somali troops took a strategic stronghold in the south-west of the country held by militant group al-Shabab, which controls parts of the country and recently merged with al-Qaeda.
Islamist insurgents who have been fighting the internationally recognised government since 2007 have said the London conference was “another attempt” to colonise Somalia.
The UK says its increased focus on the country is justified as the activities of militant groups and pirates operating off the coast of Somalia pose a direct threat to British interests in the region and to both regional and global security.
Naval ships from the UK and other countries around the world have been sent to patrol the Indian Ocean off the Somali coast to deter pirate attacks.
They have foiled a number of kidnapping attempts in recent months but attacks continue – and have been staged further from the shore.
The UK has also said it cannot rule out sending more military advisers to boost its small team currently assisting Ugandan forces part of the AU mission.
Kenya has also sent troops into Somalia to tackle al-Shabab, blaming the group for a number of kidnappings on its territory last year.
Mr Cameron told the UK Parliament on Wednesday that a more co-ordinated approach was needed by the international community to tackle the multiple challenges facing the country.
“This is about trying to put in place the building blocks among the international community but, above all, among the Somalis themselves for a stronger and safer Somalia,” he said.
“That means taking action on piracy, on hostages, to support the African Union’s mission in the country, it means… working with all parts of Somalia to try and give that country a second chance.”
Foreign Security William Hague, who visited Somalia earlier this month, says he is “realistic” about what can be achieved in a single day but a more stable Somalia would benefit the region as well as the UK.
Somali leaders have said its challenges cannot be solved by military means alone and a parallel focus is needed on boosting humanitarian aid, education and law and order.
Somalia’s prime minister told the BBC that his country was at a “crossroads” and needed a massive injection of money.
“It is at a very critical juncture in its history,” Mr Ali said. “We are moving from an era of warlordism, terrorism, extremism and piracy and we are moving into an era of peace, stability and normalcy.
“Twenty years of lawlessness, violence and chaos is enough. Somalis are ready to move on.”
But a spokesman for al-Shabab told the Somaliland Times that “Britain must realise that the Muslims have long rejected British imperialism and the futility of their renewed attempt is obvious”.
Despite being forced out of the capital, Mogadishu, last year, it has continue to stage suicide attacks in the city.