International donors have pledged $2.7 billion in aid to help Somalia rebuild after more than two decades of civil war.

The aid was announced at Monday's conference of international donors and Somali government representatives in Brussels.

The pledges were made in support of a three-year reconstruction plan, called the New Deal Compact, which is aimed at strengthening the country's political system, improving security, and continuing the gains made during the transition.

Among the donors was the European Union which pledged $870 million in support.

During her opening remarks, EU Foreign Policy Chief Catherine Ashton said the key to Somalia's success would be long-term investment.

"And this compact on its own will not resolve everything. But it gives us a plan, it gives us a set of commitments that will enable us to be focused on what we do. And if our commitment is firm, we cannot fail.''

Somali President Hassan Sheikh Mohamud said he was grateful to the European Union and the international community, but added the timing and delivery of the aid was crucial.

"The new deal must be delivered on the ground soon; it must not be a well-intentioned bureaucratic process that remains remote from the Somali lives. The expectations from our people are extremely and understandably high."

The EU has already provided $1.8 billion in development and security aid for Somalia since 2008.

About 50 high-level delegates from Africa, Europe and the United States are attending the one-day meeting in Brussels, along with international aid and development organizations.

Meanwhile, Somalia's hardline Islamist al-Shabab rebels dismissed the conference as a waste of time.

The French news agency quoted them as saying the meeting was "a bit like Belgian waffles" - sweet on the outside, but without much substance.