The United States was meeting today with countries from around the world, including its adversary Iran, to seek support for its new strategy to end a stalemate in Afghanistan.
US Secretary of State Hillary Clinton was not expected to hold substantive talks with Iranian Deputy Foreign Minister Mohammad Mehdi Akhoundzadeh at the meeting in The Hague.
But the conference would nonetheless bring the two together as Washington tries to enlist regional support in tackling Islamist militants in Afghanistan and Pakistan.
Richard Holbrooke, US special representative for Afghanistan and Pakistan, said Iran's presence at the conference was a logical part of efforts to produce peace for Afghans.
"How can you talk about Afghanistan and exclude one of the countries that's a bordering, neighbouring state?" he told reporters in The Hague. "The presence of Iran here is obvious."
Ahead of the conference, Akhoundzadeh repeated Iran's opposition to the presence of US troops in Afghanistan.
"The presence of foreign troops cannot bring peace and stability for Afghanistan," he was quoted as saying by Iran's official IRNA news agency.
"It encourages radicalism," he said. "This policy (that the Western countries) decide for the Afghan nation and for the Afghan officials does not work out any more."
Shi'ite Iran worked with Washington after the United States ousted the Sunni Taliban from Afghanistan 2001.
But it backed off after being branded by former US president George W Bush as part of the "axis of evil".
It has denied US accusations that it has supported the Taliban as a way of keeping at bay the United States, which has troops in both Iran's neighbours - Iraq and Afghanistan.
In a reversal of the policy of the former Bush administration, Obama's team views Iran as vital to any lasting solution in Afghanistan, and has sought engagement despite the continuing stand-off over Tehran's nuclear programme.
Clinton, who said she has no plans for direct talks with Iranian officials at the conference, said she wanted Iran's help on border security and fighting drugs in Afghanistan.
European Union foreign policy chief Javier Solana said he hoped Iran would "take a responsible position".
"There is no doubt that Afghanistan cannot be stable without a stable region," Solana told reporters at the forum, which was chaired by UN Secretary General Ban Ki-moon and the Dutch foreign minister.
More than 70,000 US and Nato troops are in Afghanistan battling a growing insurgency by the Taliban, which is also spreading its influence in Pakistan.
Since taking office in January, Obama has ordered 17,000 extra troops to Afghanistan to tackle violence ahead of elections, and a further 4,000 to help train the army.
Clinton announced $40m in new US aid for a UN fund to prepare for Afghanistan's election in August, and an effort to encourage other nations at the conference to provide assistance. The 27-nation European Union announced $60m in aid before the talks.
"We do want to encourage the participants to begin thinking hard about what their contributions will be," Clinton said.
Dutch organisers said 72 out of the 73 countries invited confirmed their attendance, with only Uzbekistan bowing out. With international groups and observers, the total is 87 with nearly 700 delegates attending.