Prime Minister Gordon Brown on Thursday called for international support in delivering peace and security to Afghanistan.

Brown outlined the aims of the Afghanistan Conference in London during an opening address, saying the aim of the conference, co-hosted by Britain, the United Nations and Afghanistan, was to agree on a clear international plan for the next 18 months in the war-torn country.

Earlier, the prime minister met with Afghan President Hamid Karzai, U.N. Secretary General Ban Ki-moon, NATO Secretary General Anders Fogh Rasmussen, and international representatives including U.S. Secretary of State Hillary Clinton.

"This is a decisive time for the international operation that is helping the Afghan people secure and govern their own country," Brown said. "For this conference marks the beginning of the transition process - agreeing the necessary conditions under which we can begin - district by district and province by province - the process for transferring responsibility for security from international forces to Afghan forces."

He described the shared strategy as building up Afghan institutions - the army, the police, and the government, saying that "so that as they become stronger we can hand over to them the responsibility of tackling terrorism and extremism, and our forces can start to come home.

"It will take time - but I believe the conditions set out in the plan we will sign up to today can be met sooner than many expect, and that as a result the process of handover will begin later this year," he added.

In addition, Brown said in return for the commitment, the international community must agree on Thursday with Karzai's plans for the expansion of the Afghan army and police force and pledge the necessary support to do so.

Brown also said the international community will stand united with Karzai in five areas - fighting corruption, securing stronger governance, economic development, supporting an Afghan-led peace and re-integration program and strengthening regional partnerships.