'Culture of impunity'
International rights group Human Rights Watch called for the London conference to address "widespread human rights abuses by all parties," which, it says, have been overlooked throughout the long years of conflict.
"The failure to address these abuses and the culture of impunity in which they have taken place has contributed to ongoing conflict and insecurity," the group said in a statement.
"A substantial improvement in the respect for human rights and accountability for serious abuses is now essential."
Delegates agreed on a package of support for Somalia on preventing sexual violence, the UK Foreign Office said. As part of this, a team of U.N. experts will deploy to Somalia in the summer.
Somalia was subject to international condemnation this year over a case in which a woman and a journalist were sentenced to prison after she told him she was raped by security forces. She was subsequently acquitted on appeal, but the journalist's conviction was upheld, though his sentence was cut.
Somali Prime Minister Abdi Farah Shirdon said via his Twitter account that the country's progress so far had defied the skeptics, but challenges remain.
"With the support of our friends and partners the progress must be made unstoppable. A bright future for #Somalia is within touching distance," he tweeted Monday.
Somalia has lacked an effective central government since 1991, with portions of the Horn of Africa nation left lawless.
In January, the United States granted official recognition to the new Somali government.