Washington wants the world to look into human rights abuse in other countries but is keen to halt the progress of any investigation delving into war crimes committed by Americans.
The bomb struck a bus travelling through Kandahar province. The attack is said to the third since a brief ceasefire declared by the Taliban for a major Muslim holiday that ended last month.
Skirmishes between Taliban fighters and Afghan security forces recommence after a three-day ceasefire expired in Afghanistan.
US and NATO officials said that US troop strength in Afghanistan is down to nearly 8,600, well ahead of a schedule agreed with Taliban in late February, in part because of concerns about the spread of the coronavirus.
In recent weeks in Afghanistan, militants have carried out several roadside bombings and rocket attacks in Kabul and other parts. Latest series of explosions appears to be the first coordinated effort for some months.
People were killed and wounded during a protest sparked by growing discontent at the distribution of food, allegedly favouring people with political connections.
Afghan government forces in the last two months have suffered heavy casualties across the country, threatening a fragile peace deal between the United States and the Taliban.
Taliban said, "the intentional delays in the release of our prisoners violates the peace agreement, therefore we call back our technical team back from Kabul".
The blast occurred in Helmand province where both the Taliban and Daesh are said to be active.
The peace process is going through its most intricate phase as Afghan leaders from all sides struggle to find common ground.
The apparent insider attack, which took place in Nangarhar province, occurred after a combined US and Afghan force was returning from a "key-leader engagement," Colonel Sonny Leggett, a spokesman for US forces in Afghanistan, said in a statement.
Iran has limited influence over the Taliban and little to gain from prolonging the war.
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