The April election is seen as the most crucial since the US-led overthrow of the Taliban in 2001, which brought Karzai to power.
International aid donors, who provide the bulk of Afghanistan’s income, hope a transfer of power will enable the country to move beyond years of damaging allegations of corruption and maladministration.
In an interview this month, Karzai blamed corruption on irresponsible spending by donors and said coalition troops had brought nothing but suffering because security was still poor.
Security in the country has been deteriorating, increasing worry about Afghanistan’s prospects after Western forces leave. On Saturday, a car bomb killed four people in the eastern city of Jalalabad.
Efforts to draw the Taliban into negotiations have come to nothing. The militants say they will fight on until all foreign forces leave and dismiss Karzai as a US “puppet.”
The Afghan president said the question of whether Kabul would be able to try US citizens for crimes committed on its territory could not be decided by his government.
“The issue of jurisdiction is one such issue that is beyond the authority of the Afghan government and it is only and entirely up to the Afghan people to decide upon through two mechanisms,” Karzai said, referring to the country’s traditional assembly and its parliament.
Kerry said that US troops operated under the same standards wherever they were deployed.
“Wherever our forces are found, they operate under the same standard,” he said. “We are not singling out Afghanistan.”