Bonn: The United States and other nations on Monday vowed to keep supporting Afghanistan's fragile economy after most foreign forces leave the country, as an international conference got underway in Bonn despite the crippling absence of key regional player Pakistan.

The Bonn conference is focused on the transfer of security responsibilities from international forces to Afghan security forces during the next three years, long-term prospects for international aid and a possible political settlement with the Taliban.

"Together we have spent blood and treasure in fighting terrorism," Afghan President Hamid Karzai said in his opening remarks, urging the international community to stand by the country even beyond the planned troop withdrawal in 2014.

"Your continued solidarity, your commitment and support will be crucial so that we can consolidate our gains and continue to address the challenges that remain. We will need your steadfast support for at least another decade," Karzai said.

About 100 countries and international organisations are represented among the 1,000 conference delegates, with some 60 foreign ministers in attendance, among them US Secretary of State Hillary Rodham Clinton.

"This is the beginning of our hard work," Clinton told a sideline meeting with Afghan activists, women leaders and others. "We have to be very clear about what we can and cannot do together."