Japanese Foreign Minister Koichiro Gemba, right, listens while U.S Secretary of State Hillary Rodham Clinton speaks during a press conference at the Iikura Guest House on Sunday, July 8, 2012 in Tokyo. (Brendan Smialowski/AP)

Donor nations meeting here Sunday at a conference on aid to Afghanistan pledged $16 billion over the next four years for civilian projects, from roads to schools to strengthening the rule of law, in exchange for pledges from the Afghan government to combat corruption.

The promised assistance amounts to $4 billion a year, roughly equivalent to Afghanistan’s gross domestic product. The annual amount is slightly more than the $3.9 billion infusion that the World Bank said Afghanistan needs to keep its economy from collapsing once U.S. and NATO forces withdraw by the end of 2014, taking with them jobs and other economic benefits.

U.S. Secretary of State Hillary Rodham Clinton, who arrived in Tokyo after a brief stop in Kabul, said at the conference that the Obama administration would request from Congress funding through 2017 that is “at or near” the levels the United States has provided over the past decade, which has ranged from $1 billion to $4 billion annually.

Clinton spoke of what the Afghan government and donors have optimistically branded “the transformation decade,” and of the necessity of good governance and transparency.

“We know Afghanistan’s security cannot only be measured by the absence of war,” she told the gathering of more than 70 nations and organizations. “It has to be measured by whether people have jobs and economic opportunity, whether they believe their government is serving their needs.”

The United States remains the largest donor to Afghanistan. Japan promised up to $3 billion through 2016, and Germany said it would maintain its current funding level of about $550 million a year until at least 2016.

That is about the same amount pledged by Iran, which has been accused by the United States and NATO of destabilizing Afghanistan and which committed to $500 million for road and railway construction, among other projects mainly in the western part of the country.

“We share history, culture and religion,” said Iranian Foreign Minister Ali Akbar Salehi. “We think when the foreign troops leave, Afghanistan needs assistance from its neighbors to make up for the last decade of destruction.”

Much of the talk in the gray-carpeted hallways of Tokyo’s Prince Park Tower Hotel dwelled on concerns about the rampant corruption in Afghanistan that has eaten away donor money in the past and whether fresh pledges by Afghan President Hamid Karzai to combat it — outlined in a document called the Mutual Accountability Framework — would make a difference this time.

The document includes specific goals and indicators of progress toward meeting those targets. For instance, “improved integrity of public financial management and the commercial banking sector” would be indicated by the government continuing to recover the nearly $1 billion in assets that were looted from Kabul Bank and prosecuting those involved in the scandal.

Although individual donor nations may decide on their own consequences if the goals are ignored, the document does not explicitly outline penalties.

“The enforcement is the agreement,” said a representative for Britain’s foreign aid program, who spoke on the condition of anonymity to be candid. “But the honest answer? I don’t think we’ll be saying that if we see 70 percent of the reforms, you’ll be getting 70 percent of the money. It’s just the principle of accountability, and we’ll go from there.”

Leaders from Afghan civil society groups were cautiously hopeful that the accountability measures could improve things in Afghanistan, one of the world’s 10 poorest nations.

“If the international community helps, it will be possible,” said Anayatullah Durrani, director of the Afghan Social Development Organization, which runs education programs. “But Karzai is just one person — even if he is serious, the ones under him, they are all involved in corruption.”

Durrani explained the problem by describing a situation he said he witnessed recently, in which a provincial governor asked for a $200,000 bribe out of a $2.8 million fund for an irrigation project.

“Our suggestion is the money should be spent on small projects that involve people, where people participate,” Durrani said. “If they apply the funds to big projects, the corruption will be big.”

In her remarks, Clinton emphasized the role of civil society leaders in demanding accountability from the Afghan government. And later she sat down for an hour or so with Durrani and others in a smaller conference room and listened.

“When we talk about ‘Afghan-led,’ we don’t just mean the government,” Clinton said. “We mean the Afghan people.”

Meanwhile, at least 18 civilians, including women and children, were killed in bombings in Afghanistan on Sunday. Casualties among noncombatants have been rising in recent months.

The first blast ripped through a minivan on a dirt road in the Arghistan district of southern Kandahar province near the border with Pakistan, according to Ahmad Jawed Faisal, a spokesman for the provincial governor.

A group of civilians traveling in a tractor on the same road stopped to help the casualties when the second explosion occurred, Faisal said. The third blast, also in Arghistan, killed four members of a family, he said.

Faisal said the roadside bombs were planted by Taliban-led insurgents who rely on the devices as part of their campaign against foreign and Afghan forces.

Sayed Salahuddin in Kabul contributed to this report.